Chapter 4- Earth
Chemistry
Section 1- Matter
Section 2- Combinations of Atoms
• Objectives
1.
2.
3.
4.
5.
Compare chemical properties and physical properties of
matter
Describe the basic structure of an atom
Compare atomic number, mass number, and atomic mass
Define Isotope
Describe the arrangement of elements in the periodic
table
Section 1- Matter
• Introduction
• Every object in the universe is made of particles of some
kind of substance
• Scientist use the word matter to describe the substances of
which objects are made
• Matter is anything that takes up space and has a mass
• The amount of matter in any object is the mass of that
object
• All matter has observable and measurable properties
Section 1- Matter
• Properties of Matter
• Physical Properties
• Ex; density, color, hardness, freezing point, boiling point, and
the ability to conduct an electric current
• Chemical Properties
• Ex; For Iron- Iron reacts with Oxygen to form rust
Section 1- Matter
• Properties of Matter (Elements)
• A substance that cannot be broken down into simpler, stable
substances by chemical means
• Each element has a characteristic set of physical and
chemical properties that can be used to identify it
Section 1- Matter
• Properties of Matter (Elements)
• More than 90 elements occur naturally on Earth
• About 2 dozen have been created in laboratories
• Of the natural elements 8 make up more than 98% of the
Earth’s crust
• Every known element is represented by a symbol of one or
two letters
Section 1- Matter
• Properties of Matter (Atoms)
• Elements consist of atoms
• An atom is the smallest unit of an element that has the
chemical properties of that element
• Atoms cannot be broken down into smaller particles that
will have the same chemical and physical properties as the
atom
• A single atom is so small its size is hard to imagine
Section 1- Matter
• Atomic Structure
• Subatomic Particles
• Protons (+)
• Electrons (-)
• Neutrons (no charge)
Section 1- Matter
• Atomic Structure (The Nucleus)
• Protons and Neutrons of an atom are packed close to one
another
• Together they form the nucleus, which is the small region in the
center of an atom
• The nucleus has a positive charge
• The nucleus makes up most of an atom’s mass, but very little of
the atom’s volume
Section 1- Matter
• Atomic Structure (The Electron Cloud)
• The electrons of an atom move in a certain region of space
called an electron cloud that surround the nucleus
• Because opposite charges attract each other, the negatively
charged electrons are attracted to the positively charged
nucleus
• This attraction is what holds electron in the atom
Section 1- Matter
Section 1- Matter
• Atomic Number
• The number of protons in the nucleus of an atom
• All atoms of any given element have the same atomic
number
• Elements on the periodic table are ordered according to
their atomic number
Section 1- Matter
• Atomic Mass
• The sum of the number of protons and neutrons in an atom
• Atomic Mass Unit (amu)
• Protons and Neutrons each have an atomic mass that is
close to 1 amu
Section 1- Matter
• Atomic Mass (Isotope)
• Same number of Protons
• Neutrons may differ
• An atom that has the same number of protons as other
atoms of the same element do but has a different number of
neutron is called an isotope
Section 1- Matter
• Atomic Mass ( Average Atomic Mass)
• The average atomic mass is the weighted average of the
atomic masses of the naturally occurring isotopes of an
element
Section 1- Matter
• Valence Electrons and Periodic Properties
• Based on similarities in their chemical properties, elements
on the periodic table are arranged in columns, called groups
• An atom’s chemical properties are largely determined by the
number of the outermost electrons in an atom’s electron
cloud, these electrons are called valence electrons
Section 1- Matter
• Valence Electrons and Periodic Properties
• Groups 1 &2
• The number of valence electrons in each atom is the same as
that atom’s group number
• Groups 3-12
• Have 2 or more valence electrons
• Groups 13-18
• The number of valence electrons in each atom is the same as
the atom’s group number minus 10, EXCEPT for Helium
• Group 18
• Have 8 valence electrons
Section 1- Matter
• Valence Electrons and Periodic Properties
• Elements whose atoms have only 1,2, or 3 valence electrons
tend to lose electrons easily
• These elements have metallic properties and are generally
classified as metals
• Elements whose atoms have from 4-7 valence electrons are
more likely to gain electrons
• Many of these elements, which are in Groups 13-17, are
classified as nonmetals
Section 1- Matter
Section 1- Matter
• Objectives
1.
2.
3.
4.
Define compound and molecule
Interpret chemical formulas
Describe two ways that electrons form chemical bonds
between atoms
Explain the differences between compounds and
mixtures
Section 2- Combinations
of Atoms
• Introduction
• A substance that is made of two or more elements that are
joined by chemical bonds between atoms of those elements
is called a compound
• The properties of a compound differ from those of the
elements that make up the compound
Section 2- Combinations
of Atoms
• Molecules
• The smallest unit of matter that can exist by itself and retain
all of a substance’s chemical properties
• In a molecule of two or more atoms, the atoms are
chemically bonded together
• Some molecules consist entirely of atoms of the same
element
• Some elements occur naturally as diatomic molecules,
which are molecules that are made up of only two atoms
Section 2- Combinations
of Atoms
• Chemical Formulas
• A combination of letters and numbers that shows which
elements make up a compound
• Shows the number of atoms of each element that are
required to make a molecule of a compound
• The chemical formula for water is H2O
• This indicates that each water molecule consists of two atoms
of hydrogen and one atom of oxygen
Section 2- Combinations
of Atoms
• Chemical Equations
• Elements and compounds often combine through chemical
reactions to form new compounds
• The reaction of these element and compound can be
described in a formula called a chemical equation
Section 2- Combinations
of Atoms
• Chemical Equations (Equation Structure)
• Reactants are on the left-hand side of the arrow, form the
products, which are on the right-hand side of the arrow
• When chemical equations are written the arrow means
“gives” or “yields”
CH4 + 2O2 CO2 + 2 H2O
Section 2- Combinations
of Atoms
• Chemical Equations (Balanced Equations)
• A chemical equation is balanced when the number of atoms
of each element on the right side of the equation is equal to
the number of atoms of the same element on the left side
• To balance an equation, you must put numbers called
coefficients in front of the chemical formula
Section 2- Combinations
of Atoms
• Chemical Bonds
• The forces that hold together the atoms in the molecules
• They are formed because of the attraction between positive
and negative charges
• Atoms form chemical bonds by either sharing or
transferring valence electrons from one atom to another
Section 2- Combinations
of Atoms
• Chemical Bonds (Ions)
• An atom or molecule that has gained or lost one or more
electrons and has a negative or positive charge
Section 2- Combinations
of Atoms
• Chemical Bonds (Ionic Bonds)
• The attractive force between oppositely charged ions, which
form when electrons are transferred from one atom or
molecule to another
• Most ionic compounds form when electrons are transferred
between the atoms of metallic and nonmetallic elements
Section 2- Combinations
of Atoms
• Chemical Bonds (Covalent Bonds)
• A bond formed when atoms share one or more pairs of
electrons
• When atoms share electrons , the positive nucleus of each
atom is attracted to the shared negative electrons.
Section 2- Combinations
of Atoms
• Chemical Bonds (Polar Covalent Bonds)
• A covalent bond in which the bonded atoms have an
unequal attraction for the shared electrons
Section 2- Combinations
of Atoms
• Mixtures
• A combination of two or more substances that are not
chemical combined
• Substances that make up a mixture keep their individual
properties
• Unlike compounds, a mixture can be separated into its parts
by physical means
Section 2- Combinations
of Atoms
• Mixtures (Heterogeneous Mixtures)
• Mixtures in which two or more substances are not
uniformly distributed
Section 2- Combinations
of Atoms
• Mixtures (Homogeneous Mixtures)
• A homogeneous mixture of two or more substances that are
uniformly dispersed throughout the mixture is a solution
Section 2- Combinations
of Atoms
•Questions
?’s
Chapter 4- Earth
Chemistry