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Chemistry Study Guide
Atoms and Subatomic Particles
 Atom. Al matter is made up of unique particles called atoms. An atom contains:
o Protons- Positively charged; have atomic mass of one; Located in the nucleus
of the atom.
o Neutrons- Neutral in charge; the same mass as the proton; also located in the
nucleus of the atom.
o Electrons- Negatively charged; they move around the nucleus at high speeds
on electron rings; same number as protons.
Atomic Notation
 Atomic Symbol- Scientists use a symbol of one or two letters to identify
elements. The first letter is always capitalized, but not the second. Examples: H,
O, He, Fe
 Atomic Number- The number of protons an atom has; also equals the number of
electrons of the uncharged atom.
 Atomic Mass- The number of protons and neutron in an atom.
Elements and Compounds
 Elements- Any form of matter made up of identical atoms. Examples: carbon,
oxygen.
 Compounds- A substance made up of atoms of different elements joined
chemically together. These elements are always combined in fixed proportions.
Examples: water, salt, sugar
 Molecule- A group of atoms that share one or more pairs of electrons; the
smallest part of a compound with its properties.
Chemical Reactions
 Chemical Reactions- These are combinations of divisions of substances that result
in one or more new substances with new physical and chemical properties.
 Chemical Equations- There should be the same number of atoms on each side of
the equation. Multiply the atoms in each molecule by the number of molecules to
see that they balance: 2H2 + O2  2H2O
 Conservation of Mass- Mass cannot be created or destroyed in a chemical
reaction.
Physical and Chemical Properties
 Physical Properties- every type of matter has its own physical properties. These
include its color, odor, density (mass/volume), hardness, melting and boiling
point, and how well it conducts heat and electricity. A physical property can
change wiout changing a substance’s chemical make-up (arrangement of atoms).
 Chemical Properties- Chemical properties refer to the ability of a substance to
react with other forms of matter. For example, some substances are flammable. If
they are heated with oxygen, they will react and burst into flames. The ability of a
substance to combine with oxygen is an example of chemical property.
Periodic Table of the Elements
Table of elements arranged by their atomic number – the number of protons. An elements
position on the table will show many of its general properties
 Periods- The table is arranged in horizontal rows called periods. The period tells
you how many electron energy levels the atom has.
 Groups- Vertical columns whose members of the same group have similar
chemical and physical properties.
o Have the same number of outer electrons.
o Often share other characteristics like the ability to conduct electricity or heat
Compound, Mixtures and Solutions
 Compound- Made of two or more elements chemically combined. The elements
in a compound are always in the same proportion. The properties of the
compound differ from the elements that make it up.
 Mixture- Two or more substances mixed together without chemically combining.
The substances can be separated without a chemical reaction.
 Solution- A mixture in which one substance is dissolved uniformly in another
substance.
Elements
 Metals- Hard, shiny elements appearing on the left side of the Periodic Table.
They are good conductors of heat and electricity. Examples include; iron (Fe),
aluminum (Al), and sodium (Na).
 Metalloids- Appear alon the bolded line on the Periodic Table. They conduct
electricity under some conditions. Examples include; boron (B) and silicon (Si).
They are important to the semiconductor industry.
 Nonmetals- These appear to the right of the Periodic Table. They are poor
conductors of heat, and do not conduct electricity. Many are gases, or brittle
solids. Examples include: carbon (C) oxygen (O), and sulfur (S).
 Nobel Gases- Appear to the far right of the Periodic Table. (Group 18). They do
not usually combine with other substances. Examples include: argon (Ar) and
neon (Ne).
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