Chapter 5 Notes (to section 5.5)
Matter - is anything that has mass and takes up space. So chemistry is the study of almost everything
Substance -
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a particular kind of matter that has a uniform and definite composition.
(i.e. Sugar is a substance whereas soda is not)
matter can exist in three different states: solid, liquid, and gas
(Be able to define and describe 3 states)
Properties of Matter
all samples of substances have identical properties/ distinguishing features
Mixtures consist of a physical blend of two or more substances. A mixture has variable composition and may be
classified as homogeneous or heterogeneous.
heteros = different, genos = kind, homo = same
✓
Be able to compare and contrast homogeneous/heterogeneous mixtures
Homogeneous
* Parts of the mixture are evenly distributed.
* Aka solutions (solute is dissolved in solvent)
Examples:
Sugar (solute) and Water (solvent)
Salt (solute) and Water (solvent)
Heterogeneous
* Parts of the mixture are not evenly distributed.
* Aka a mechanical mixture
Examples:
- Salt and Pepper
- Oil and Water
- Unshaken salad dressing
By separating mixtures into their components we break them into their purest forms....... elements and
compounds
Element
a substance composed of only one type of atom. They can not be broken down
into simpler form. They are the building blocks of all other substances.
Carbon only has carbon atoms, sulfur only has sulfur atoms
Compound
a chemical substance composed of 2 or more atoms in definite ratios. It can be broken
down into its simplest parts by a chemical reaction.
CO2 is a gas composed of carbon and oxygen; for every 1 carbon atom there are 2 oxygen atoms
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the chemical and physical properties of compounds are quite different from those of their
component elements. (Ex: sugar/ table salt)
Physical Properties
color
boiling point
freezing point
mass
density
texture
physical change
VS.
- physical changes are
reversible
- doesn’t require heat
- change in state
- mass and energy conserved
- key words: cutting, grinding
bending
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Chemical Properties
How a substance reacts:
Corrosive (reacts with metal);
flammable (reacts with fire);
caustic (reacts with skin);
reacts violently with air or water
chemical change
- chemical changes are not easily
reversed
- generally requires heat
- change in composition
- mass and energy conserved
- key words: rot, rust, decompose
grow, decay, sprout
Physical changes of a substance will alter the substance without changing its composition. (Cutting,
grinding, melting, freezing). A chemical change, however, will alter the substances’ identity
Elements
Every element is represented by a chemical symbol. The chemical symbols are a kind of scientific
alphabet. Chemical symbols are used to write chemical formulas which tells us the elements and the
proportions of each.
Example 1.
The chemical symbol for Hydrogen is H; while the chemical symbol for Gold is Au.
Example 2.
The chemical symbol for sugar (glucose) is C6 H12 O6. This means that each molecule of glucose has 6
C-atoms, 12 H-atoms, and 6 O-atoms.
The Periodic TableDmitri Mendeleev (1834-1907) sequenced the elements in increasing atomic mass. Because Mendeleev’s
arrangement highlighted periodic (repeating) patterns of properties, it was called a periodic table.
The modern periodic table organizes the elements according to atomic number.
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Combinations of these elements make compounds
An elements position on the periodic table is characteristic of the element
Metals are found on the left-hand side of the table
Non-metals are found on the right-hand side of the periodic table
Be able to compare metals and non-metals (see page 185 in your text).
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The table is organized in rows and columns according to similarities in their properties.
Elements are arranged in 7 numbered periods (horizontal rows) and 18 numbered groups (vertical
columns).
Know terms:
Representative elements Metals
(high luster when clean, high electrical conductivity, are ductile, are malleable)
Transition metals
Inner transition metals
Nonmetals
(nonlustrous, poor conductors of electricity,
Semimetals or metalloids
(elements with the properties of both metals and nonmetals)
alkali metals (Group 1)
alkaline earth metals (Group 2)
halogens (Group 17 or 7 in some texts)
noble gases (Group 18 or 8 in some texts)
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Elements and Atomic Structure
Atoms are the basis of chemistry and the basis of everything in the universe. Remember all
matter is composed of atoms!
Atom – smallest particle of an element that still retains the properties of that element
the atom is a microscopic structure. It is similar to the cell in biology. Like the cell the atom can
be broken down into it simplest parts as well.
• Atoms can be broken down into electrons, protons, and neutrons.
Electrons are negatively charged subatomic particles. Symbol is e- . (J.J. Thompson)
Protons are positively charged subatomic particles. (Rutherford)
Neutrons are subatomic particles with no charge. (James Chadwick)
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The proton & neutron are found in the center of the atom, a place called the nucleus.
The electrons orbit the nucleus.
Protons
• Protons are very important because they help determine the identity of an element
• They are inside the nucleus
• They have a positive charge +
• Atom Identity – the number of protons an atom has will determine its identity.
Neutrons
• Found inside the nucleus
• Have a neutral charge
• Have a relative mass of 1 atomic unit
• Important for creating isotopes (coming soon!)
Electrons
• Found outside the nucleus
• Forms an orbital cloud (the location where an electron might be found)
• Has a negative charge –
Different elements have different numbers of subatomic particles thus giving different elements different
characteristics/properties
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So how do we know how many subatomic particles an element has?
Every element on the table has an atomic number. The atomic number is the number of protons
and it is also the number of electrons in an atom of an element. Every element has a mass number
(neutral elements) which is formed by adding the number of protons and neutrons – as a result the
mass of an element comes from the nucleus (where the protons and neutrons are located).
# of protons = atomic number
# of neutrons = mass number - atomic number
# of electrons = number of protons (When the atom is neutral)
Neils Bohr (1913) –
• Electrons move around the nucleus in paths called orbitals
• Each electron in an orbit has a definite amount of energy ; further away from nucleus = greater
energy
• Electrons cannot exist between orbits, but they can move up or down from one orbit to another
• Electrons are more stable when they are at lower energy (closer to the nucleus)
Bohr-Rutherford diagrams are a common way to show the arrangement of electrons in an atom.
Circles are drawn around the atomic symbol; each circle represents an energy level; the dots represent
electrons that occupy each energy level.
The first ring can contain a maximum of 2 electrons, the second energy level a max of 8 electrons. The third has
a maximum of 18 electrons but for now, only has 8 electrons.
The outer shell of an atom is called the valence shell and the electrons in this shell are called valence electrons. They
will be important as these electrons are the ones responsible for reactivity, bonding etc.
Atoms by themselves are neutral (have no charge). The number of protons and electrons are balanced or equal. What
happens if an atom loses or gains an electron? It becomes an ION.
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Ion – charged atom in which the number of electrons is different from the number of protons due to a loss or gain
of electrons
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Positive ions are called cations
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Negative ions are called anions
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Ionic Charge – numerical value of the electric charge with a + or –. Formed by the difference between the number
of protons and electrons
Examples: Al3+, F1-,S2-
Note: When nonmetals gain electrons to form ions the name of the ion changes its ending to “ide” (E.g. F- ion is called a
fluoride ion)
Examples:
1. Ca is a calcium atom. Ca2+ is a CALCIUM ion (cation). It LOST 2 electrons. The ending of the name stays the same
with cations!
2. I is an iodine atom. I1- is an iodide ion (anion). Iodine gained 1 ELECTRON. The ending changes with anions!