What are elements?
What are elements?
• The physical world that surrounds you and all
living things are composed of matter.
• Matter is anything that has volume and mass.
• On Earth, matter usually can be found as a solid,
liquid, or gas.
What are elements?
Elements
• All matter is made of substances called
elements.
• An element is a substance that cannot be broken
down into simpler substances by physical or
chemical means.
• Ninety-two elements occur naturally on Earth
and in the stars.
• Other elements have been produced in
laboratory experiments.
What are elements?
Elements
• Each element is identified by a one-, two-,
or three-letter abbreviation known as a
chemical symbol.
What are elements?
Elements are Made of Atoms
• Each element has distinct characteristics.
• An atom is the smallest particle of an element
that has all of the characteristics of that element.
• All atoms consist of even smaller particles:
protons, neutrons, and electrons.
What are elements?
Elements are Made of Atoms
• The nucleus, which is made up of protons and
neutrons, forms the center of an atom.
– A proton (p+) is a tiny particle that has mass and a
positive electrical charge.
– A neutron (n0) is a particle with about the same mass
as a proton, but it is electrically neutral; that is, it has
no electrical charge.
• All atomic nuclei have a positive charge.
What are elements?
Elements are Made of Atoms
• The number of protons and neutrons in different
atoms varies widely.
– The atomic number is the number of protons in an
atom’s nucleus.
– The mass number is the combined number of protons
and neutrons.
What are elements?
Elements are Made of Atoms
What are elements?
Elements are Made of Atoms
• Surrounding the nucleus of an atom are smaller
particles called electrons.
• An electron (e–) has little mass, but it has a
negative electrical charge that is exactly the same
magnitude as the positive charge of a proton.
• An atom has an equal number of protons and
electrons which produces an atom that has no
overall charge.
What are elements?
Elements are Made of Atoms
• An energy level represents the area in an atom
where an electron is most likely to be found.
• The mass of an atom depends mostly upon the
number of protons and neutrons in its nucleus.
• The size of an atom
depends upon the
number and
arrangement of
its electrons.
What are elements?
Electrons in Energy Levels
• Electrons are distributed over one or more
energy levels in a predictable pattern.
• Each energy level can hold only a limited
number of electrons.
– The innermost energy level can hold only 2 electrons.
– The second energy level can hold up to 8 electrons.
– The third energy level can hold up to 18 electrons.
– The fourth energy level can hold up to 32 electrons.
• Electrons tend to occupy the lowest available
energy level.
What are elements?
Electrons in Energy Levels
• The number of electrons in the outermost
energy level determines the chemical behavior
of the different elements.
• Valence electrons are the outermost electrons in
an atom.
• Elements with the same number of valence
electrons have similar chemical properties.
What are elements?
Electrons in Energy Levels
• Sodium (Na) atoms, with just one valence
electron, are highly reactive metals, which
means that they combine easily with other
elements.
What are elements?
Electrons in Energy Levels
• Elements such as helium (He), neon (Ne), and
argon (Ar) are inert, which means that they do
not easily combine with other elements.
• This is because they have full outermost
energy levels.
What are elements?
Isotopes
• The number of neutrons in the nuclei of an
element’s atoms can vary.
• Isotopes are atoms of the same element that
have different mass numbers and the same
chemical properties.
• The atomic mass
of an element is the
average of the
mass numbers of
the isotopes of an
element.
What are elements?
Isotopes
• The nuclei of some isotopes are unstable and
release radiation.
• Radioactivity is the spontaneous process
through which unstable nuclei emit radiation.
• During radioactive decay, a nucleus can lose
protons and neutrons, change a proton to a
neutron, or change a neutron to a proton.
• Because the number of protons in a nucleus
identifies an element, decay changes the
identity of an element.
What are elements?
What Elements are Most Abundant?
• The two most abundant elements in the universe
are hydrogen and helium.
What are elements?
What Elements are Most Abundant?
• The percentages of elements in Earth’s crust
differ from the percentages in the universe.
What are elements?
WARM UP - you have until 2:15
• Copy down the vocabulary words below. All can
be found in the glossary!
• Take one of the blue books on your desk and
write your name in the front cover and place it in
your notebook in the hand out section.
• Take a Adopt an atom work sheet and place it in
your notebook as well.
Vocabulary
– energy level
– element
– neutron
– valence electron
– atom
– atomic number
– isotope
– nucleus
– mass number
– atomic mass
– proton
– electron
– radioactivity
How Atoms Combine
Objectives
• Describe the chemical bonds that unite atoms to
form compounds.
• Relate the nature of chemical bonds that hold compounds
together to the physical structures of compounds.
• Distinguish among different types of mixtures
and solutions.
Vocabulary – copy down! Until 2:15
– compound
– ion
– solution
– chemical bond
– ionic bond
– acid
– covalent bond
– chemical
reaction
– base
– molecule
What are elements?
REVIEW Electrons in Energy Levels
What are elements?
REVIEW Section Assessment
1. Match the following terms with their definitions.
___
A proton
___
D energy level
___
C neutron
___
B atom
A. a tiny particle that has
mass and a positive
electrical charge
B. the smallest particle of an
element that has all of the
characteristics of that element
C. a tiny particle that has mass
and is electrically neutral
D. an area of an atom where
an electron is most likely to
be found
How Atoms Combine
Compounds
• A compound is a substance that is
composed of atoms of two or more different
elements that are chemically combined.
• Most compounds have totally different
properties from the elements they are made
of.
• For most elements, an atom is chemically stable
when its outermost energy level is full.
• Chemical bonds are the forces that hold the
elements together in a compound creating a
state of stability.
How Atoms Combine
Compounds
Covalent Bonds
– One way in which atoms fill their outermost energy
levels is by sharing electrons.
– A covalent bond is the attraction of two atoms for a
shared pair of electrons that holds the atoms
together.
How Atoms Combine
Compounds
Covalent Bonds
– A molecule is composed of two or more atoms held
together by covalent bonds.
– Molecules have no overall electrical charge b/c the
number of electrons is equal to total number
of protons.
How Atoms Combine
Compounds
Covalent Bonds
How Atoms Combine
Compounds
Polar Molecules
– When atoms in a covalent bond do not share
electrons equally, they form polar bonds.
– Polar bonds have
a positive end and
a negative end.
– The overall shape
of a molecule
indicates whether
it is polar.
How Atoms Combine
Ions
• Sometimes, atoms gain or lose electrons
from their outermost energy levels.
• A charged particle called an ion is an atom
that gains or loses an electron.
• In general, an atom in which the outermost
energy level is less than half-full tends to
lose its valence electrons.
• When an atom loses its valence electrons, it
becomes positively charged.
How Atoms Combine
Ions
• An atom in which the outermost energy level is
more than half-full tends to fill its outermost
energy level by adding one or more needed
electrons.
• Such an atom forms a negative ion.
• If the outermost energy level is exactly halffull, an atom may form either a positive or
negative ion.
How Atoms Combine
Ions
Ionic Bonds
– Positive and negative ions attract each other.
– An ionic bond is the attractive force between two
ions of opposite charge.
– Positive ions are always written first in
chemical formulas.
How Atoms Combine
Chemical Reactions
• Sometimes, compounds break down into
simpler substances.
• A chemical reaction is the change of one or
more substances into other substances.
• Chemical reactions are described by
chemical equations.
• A chemical equation must be balanced by
showing an equal number of atoms for each
element on each side of the equation.
How Atoms Combine
Mixtures and Solutions
• A mixture is a combination of two or more
components that retain their identities.
• When a mixture’s components are easily
recognizable it is called a heterogeneous
mixture.
– Example: Soil
• In a homogeneous mixture the component
particles cannot be distinguished, even though
they still retain their original properties.
– Example: Coffee
How Atoms Combine
Mixtures and Solutions
• A homogeneous mixture is also called a solution.
• A solution may be liquid, gaseous, or solid.
– EXAMPLES:
– Seawater is a liquid solution consisting of water
molecules and ions of many elements that exist
on Earth.
– Air is a solution of gases, mostly nitrogen and oxygen
molecules together with other atoms and molecules.
– Bronze is a solid solution of copper and tin atoms.
How Atoms Combine
Mixtures and Solutions
Acids and Bases
– Many chemical reactions that occur on Earth involve
solutions called acids and bases.
– An acid is a solution containing a substance that
produces hydrogen ions (H+) in water.
– The most common acid in our environment is carbonic
acid, which is produced when carbon dioxide is
dissolved in water by the following reaction.
H2O + CO2  H2CO3
How Atoms Combine
Mixtures and Solutions
Acids and Bases
– The most common acid in our environment is carbonic
acid, which is produced when carbon dioxide is
dissolved in water by the following reaction.
H2O + CO2  H2CO3
– Some of the carbonic acid molecules in the water
dissociate, or break apart, into hydrogen ions and
bicarbonate ions, as represented by the following
equation.
H2CO3  H+ + HCO2–
How Atoms Combine
Mixtures and Solutions
Acids and Bases
– Bases produce hydroxide ions (OH–) in solution.
– A base can neutralize an acid by combining with
hydrogen ions of the acid to form water through the
following reaction.
H+ + OH–  H2O
– The pH scale measures the hydrogen and hydroxide
ions in solutions on a scale of 0 to 14, with 7 being
neutral.
How Atoms Combine
Mixtures and Solutions
Acids and Bases
– The pH scale measures the hydrogen and
hydroxide ions in solutions on a scale of 0 to 14,
with 7 being neutral.
– A solution with a pH reading below 7 is considered
to be acidic.
– A solution with a reading above 7 is considered to
be basic.
How Atoms Combine
Section Assessment
1. Match the following terms with their definitions.
___
C covalent bond A. an atom that gains or loses an
___
D compound
___
A ion
___
B acid
electron and becomes electrically
charged
B. a solution containing a substance
that produces hydrogen ions in water
C. an attraction of two atoms for a
shared pair of electrons that hold the
atoms together
D. a substance that is composed of
atoms of two or more different
elements that are chemically
combined
How Atoms Combine
Section Assessment
2. Identify whether the following are acidic, basic,
or neutral.
A Milk
___
A. Acidic
C Distilled water
___
B. Basic
A Rainwater
___
C. Neutral
B Ammonia
___
A Lemon
___
A Tomato
___
B Antacid
___
How Atoms Combine
Section Assessment
3. Describe the following chemical equation:
S + O2 SO2
One sulfur atom reacts with one oxygen
molecule to yield one molecule of sulfur dioxide.
States of Matter
Objectives
• Describe the states of matter on Earth.
• Explain the reasons that matter exists in these states.
• Relate the role of thermal energy to changes of state
in matter.
Vocabulary
• crystalline structure
• plasma
• glass
• condensation
• evaporation
• sublimation
States of Matter
Solids
• Solids are substances with densely packed
particles, which may be ions, atoms, or
molecules, depending upon the substance.
• The particles of a solid are arranged in a definite
pattern; thus, a solid has both a definite shape
and a definite volume.
• Most solids have a crystalline structure, in
which the particles are arranged in regular
geometric patterns.
States of Matter
Solids
• Crystals form symmetrical solid objects with flat
faces and straight edges between faces.
• The angles between the faces depend upon the
internal arrangement of the particles.
States of Matter
Solids
• When many crystals form in the same space
at the same time, mutual interference results
in a mass of intergrown crystals, called a
polycrystalline solid.
• Most solid substances on Earth, including rocks,
are polycrystalline materials.
• Glasses are solids that consist of densely
packed atoms arranged at random.
• Glasses do not form crystals, or their crystals
are so small that they cannot be seen.
States of Matter
Liquids
• The atoms in solids vibrate at any temperature
above absolute zero (2273°C).
• These thermal vibrations increase with increasing
temperature.
• At the melting point of the material, the vibrations
break the forces holding the solid together.
• The particles can then slide past each other, and
the substance becomes liquid.
• While liquids do not have their own shape, they do
have definite volume.
States of Matter
Gases
• Individual particles in a liquid may gain sufficient
energy to escape the liquid.
• Evaporation, or vaporization, is the process of
changing from a liquid to a gas.
• When any liquid reaches its boiling point, it
vaporizes quickly and becomes a gas.
• Sublimation is the slow change of state from a
solid to a gas without an intermediate liquid state.
States of Matter
Gases
• In gases, the particles are separated by relatively
large distances and move about at extremely
high speeds.
• Gas particles move independently of each other
and travel randomly.
• Gases have no definite shape or volume and
can expand into any space available, unless
they are restrained.
• Earth’s gravity keeps the gases in the atmosphere
from escaping into space.
States of Matter
The Electromagnetic Spectrum
• Satellites detect different wavelengths of energy
reflected or emitted from Earth’s surface.
• This energy has both electric and magnetic
properties and is referred to as electromagnetic
radiation.
• Electromagnetic radiation includes visible light,
gamma rays, X rays, ultraviolet waves, infrared
waves, radio waves, and microwaves.
States of Matter
Plasma
• At temperatures greater than 5000°C, the
collisions between particles are so violent that
electrons are knocked away from atoms.
• Such extremely high temperatures exist in stars,
and, as a result, the gases of stars consist
entirely of positive ions and free electrons.
• Plasmas are hot, highly ionized, electrically
conducting gases.
States of Matter
Changes of State
• Solids melt when they absorb thermal energy and
their temperatures rise.
• When a liquid absorbs thermal energy from the
environment, it evaporates.
• When a liquid freezes, the same thermal energy
is then released back into the environment.
• When a gas is cooled, it releases thermal energy
in the process of condensation.
• Condensation is the change from a gas to
a liquid.
States of Matter
Conservation of Matter and Energy
• The law of conservation of matter states that
matter cannot be created or destroyed but can
change from one form to another.
• The law of the conservation of energy, also called
the first law of thermodynamics, states that
energy cannot be created or destroyed but it can
be changed from one form to another.
States of Matter
Section Assessment
1. Match the following terms with their definitions.
___
C crystalline structure A. solids that consist of densely
packed atoms arranged at
___
A glasses
random
___
D evaporation
B. a slow change from a solid
___
B sublimation
to a vapor without an
intermediate liquid state
C. a solid in which the particles
are arranged in regular
geometric patterns
D. the process of change from
a liquid to a gas
States of Matter
Section Assessment
2. What are two examples of matter in the plasma
state that you have seen?
Lightning and the matter inside a neon tube are
in the plasma state.
States of Matter
Section Assessment
3. Identify whether the following processes absorb
or release energy into the environment.
___
B condensation
A. Absorb energy
___
A evaporation
B. Release energy
___
A melting
C. Neither release
or absorb
___
B freezing
___
A sublimation
Chapter Resources Menu
Study Guide
Section 3.1
Section 3.2
Section 3.3
Chapter Assessment
Image Bank
Section 3.1 Study Guide
Section 3.1 Main Ideas
• The basic building blocks of matter are atoms. Atoms consist
of protons, neutrons, and electrons.
• Protons have a positive electrical charge, electrons have a
negative electrical charge, and neutrons are electrically
neutral. Protons and neutrons make up the nucleus of an
atom; electrons surround the nucleus in energy levels.
• An element is a substance consisting of atoms with a specific
number of protons in their nuclei. Isotopes of an element differ
by the number of neutrons in their nuclei. Many elements are
mixtures of isotopes.
• The number of electrons in the outermost energy levels of
atoms determines their chemical behavior. Elements with the
same number of electrons in their outermost energy levels
have similar chemical properties.
Section 3.2 Study Guide
Section 3.2 Main Ideas
• Atoms of different elements combine to form compounds.
• Atoms held together by the sharing of electrons in covalent
bonds form molecular compounds.
• Ions are electrically charged atoms or groups of atoms.
Positive and negative ions attract each other and form ionic
compounds.
• Acids are solutions containing hydrogen ions. Bases are
solutions containing hydroxide ions. Acids and bases can
neutralize each other.
• A mixture is a combination of components that retain their
identities. A solution is a mixture in which the components can
no longer be distinguished as separate. Solutions can be
liquid, solid, gaseous, or combinations.
Section 3.3 Study Guide
Section 3.3 Main Ideas
• Matter on Earth exists in three common physical states: solid,
liquid, or gaseous. Matter in the universe includes plasma.
• Most solids have a crystalline structure.
• Liquids are densely packed arrangements of particles.
• Gases consist of widely separated, individual particles.
Plasmas are hot, highly ionized, electrically conducting gases.
• Changes of state involve thermal energy.
Chapter Assessment
Multiple Choice
1. Which of the following is NOT about elements?
a. They cannot be broken down into simpler
substances by physical or chemical means.
b. There are 47 naturally occurring elements
on Earth and in the stars.
c. All matter is made of elements.
d. Each element is identified by a
chemical symbol.
There are 92 elements that occur naturally on Earth and
in the stars.
Chapter Assessment
Multiple Choice
2. An element’s atomic number represents ____.
a. the number of protons in the atom’s nucleus
b. the combined number of protons and neutrons
in the atom’s nucleus
c. the number of neutrons in the atom’s nucleus
d. none of the above
The combined number of protons and neutrons is the
element’s mass number. The number of neutrons can
vary among the atoms of an element, creating isotopes.
Chapter Assessment
Multiple Choice
3. Which is the most abundant element in
the universe?
a. oxygen
c. iron
b. helium
d. hydrogen
Hydrogen makes up about 93.5% of all matter in the
universe. It is followed by helium at 6.3%.
Chapter Assessment
Multiple Choice
4. Which is the most abundant element in
Earth’s crust?
a. hydrogen
c. oxygen
b. silicon
d. aluminum
Oxygen makes up 46.65 of Earth’s crust. It is followed by
silicon (27.7%), aluminum (8.1%), and iron (5.0%).
Chapter Assessment
Multiple Choice
5. Which of the following is a molecule?
a. argon
c. nitrogen
b. water
d. uranium
Argon, nitrogen, and uranium are elements.
Chapter Assessment
Short Answer
6. What condition is necessary for matter to be in
a plasma state?
The temperature must be greater than
5000ºC. At temperatures this high, the
collisions between particles are so violent that
electrons are knocked away from atoms.
Chapter Assessment
Short Answer
7. What three forms can a solution take?
A solution may be liquid, gaseous, or solid.
Chapter Assessment
True or False
8. Identify whether the following statements are
true or false.
______
false A pH value of 11 would indicate an acid.
______
true Ions are atoms that either lost or gained
an electron.
______
true Apple juice is an example of a solution.
______
false In a polar bond, electrons are shared equally.
______
false Two negative ions will join to create an
ionic bond.
Image Bank
Chapter 3 Images
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Image Bank
Chapter 3 Images
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