 ATOMS, MOLECULES, and IONS
 Dalton: Proposed atomic theory with these postulates:
- Elements are composed of atoms
- All atoms of an element are identical
- In chemical reactions atoms are not changed.
- Compounds are formed when atoms of elements
combine
 Law of constant composition: the kinds and numbers of
atoms are constant for a given compound( water is 2
Hydrogen atoms and 1 Oxygen atom)
 Law of conservation of mass: during a chemical reaction,
the total mass before reaction is equal to the total mass
after reaction
 Law of multiple proportions: if 2 elements combine to
form more than 1 compound, the masses that combine
will be in a ratio of small whole numbers( water has 8
grams of oxygen per 1 gram of Hydrogen, hydrogen
peroxide has 16 grams of Oxygen per gram of Hydrogen)
 Atoms consist of protons, neutrons, and electrons.
Protons and neutrons reside in the nucleus, electrons in a
cloud around the nucleus.
 Atomic number= number of protons
 Mass number= protons + neutrons
 Isotopes have the same atomic number but a different
mass number
 Periodic table is the arrangement of elements in order of
increasing atomic number. Elements with similar
properties are placed in vertical columns called periodic
groups. Rows in the periodic table are called periods.
 Metallic elements are located on the left side of the table.
Metals tend to be malleable, lustrous, ductile, good
thermal and electrical conductors.
 Nonmetallic elements are located on the right hand side of
the table. Nonmetals tend to be brittle, dull, and do not
conduct heat or electricity well.
 The in-between elements are called metalloids.
 Molecules are the combination of 2 or more atoms. Each
molecule has a chemical formula that describes what
atoms are in the molecule and in what proportions.
Molecular formulas give the actual number and types of
atoms. The empirical formula gives relative number and
types of atoms(lowest whole number ratio)
 Atoms are neutral( protons=electrons). If electrons are
added or removed from an atom , ions are formed. Losing
electrons creates a cation(positively charged). Gaining
electrons creates an anion(negatively charged)
 When molecules lose electrons, polyatomic ions are
formed(SO42- , NO3-)
 Group 1A will lose one electron; Group 2A will lose 2
electrons; Group 3A will lose 3 electrons.
 Group 6A will gain 2 electrons; Group 7A will gain one
electron; Group 5A will gain 3 electrons.
 Naming Rules:
1. Cations formed from metals have the same name as
the metal. Na+= sodium ion; If more than one cation
can be formed, then the charge is parentheses.
Cu+=copper(I); Cu2+=copper(II). Cations formed
from nonmetals end in –ium. NH4+=ammonium ion
2. Anions end in –ide. Cl-=chloride ion
3. Polyatomic anions containing oxygen end in –ate or
–ite(more oxygen uses –ate) NO3-=nitrate; NO2=nitrite
4. Ionic compounds are named cation then anion.
BaBr2= barium bromide
5. In naming acids if the anion ends in –ide the acid
ends in –ic; -ate becomes –ic; -ite becomes –ous
6. The most metallic element is usually written first.