Chapter 2 Atoms, Molecules, and Ions

Chapter 2 Atoms, Molecules, and Ions

The Atomic Theory of Matter

Dalton’s atomic theory of matter:

1) Each element is composed of extremely small particles called atoms
2) All atoms of a given element are identical; the atoms of different elements are different and have different properties
3) Atoms of an element are not changed into different types of atoms by chemical reactions
4) Compounds are formed when ato0ms of more than one element combine

explains the law of constant composition, law of conservation of mass

The Discovery of Atomic Structure

subatomic particles – what atoms are composed of
Like charges repel each other; unlike charges attract

Cathode Rays and Electrons

cathode rays – radiation resulting from a high voltage
cause certain materials to give off light (fluoresce)
mass of an electron 9.10939*10^-28g
2000 times smaller than hydrogen

1.2.2 Radioactivity

radioactivity – spontaneous emission of radiation
three types of radiation: alpha (a ), beta (b ), gamma (g )
alpha and beta radiation are affected by an electric field
beta particles have a charge of 1-
alpha particles have a charge of 2+
gamma radiation has no particles and no charge

1.2.3 The Nuclear Atom

Rutherford determined that there was a nucleus in every atom
Protons discovered by Rutherford in 1919
Neutrons discovered by James Chadwich in 1932

The Modern View of Atomic Structure

charge of an electron is –1.602*10^-19
charge of a proton is +1.602*10^-19
1.602*10^-19 is called to electronic charge

Particle

Charge

Mass (amu)

Proton

Positive

1.0073

Neutron

None

1.0087

Electron

Negative

5.486*10^-4

atomic mass unit (amu) – equals 1.66054*10^-24 grams

angstrom (Å) – unit of length to measure atomic dimensions

1 angstrom = 10^-10m

atoms have diameters of 1-5 Å

nucleus – diameter of 10^-4 Å

Isotopes, Atomic Numbers. and Mass Numbers

all atoms of an element have the same number of protons in the nucleus

isotopes - atoms of the same element that have a different number of neutrons

atomic number – the number of protons in an atom

mass number – number of protons + number of neutrons

nuclide – atom of a specific isotope

The Periodic Table

periodic table – the arrangement of all the elements by atomic number and similarities into a table
columns = groups

metallic elements – all elements on the left side and in the middle of the periodic table

nonmetallic elements – elements on the periodic table that are divided by a diagonal steplike line from boron to astatine

metalloids – properties of metals and nonmetals

Molecules and Molecular Compounds

molecule – two or more atoms bonded together

Molecules and Chemical Formulas

chemical formula – way of representing molecules

diatomic molecule – any molecule made up of two atoms

molecular compounds – contains more than one type of atom

Molecular and Empirical Formulas

molecular formulas – chemical formulas that indication the actual number of atoms

empirical formula – chemical formulas that only give the relative number of atoms

Picturing Molecules

structural formulas – shows which atoms are attached to other atoms

perspective drawing – gives an idea of the three-dimensional shape of a molecule

ball-and-stick models – shows atoms as balls bonded by sticks

space-filling model – accurate representation of what atoms would look like

Ions and Ionic Compounds

ion – charged particle formed by the removal or addition of an electron

cation – ion with a positive charge

anion – ion with a negative charge
metal atoms tend to lose electrons
nonmetal atoms tend to gain electrons

polyatomic ions – joined atoms that have a net positive or negative charge

Predicting Ionic Charges

alkalie metals form 1+ ions
alkaline earth from 2+ ions
halogens form 1- ions
group 6A from 2- ions

Ionic Compounds

ionic compound – a compound that contains positively and negatively charged ions
ionic compounds are generally combinations of metals and nonmetals
molecular compounds are generally nonmetals only

Naming Inorganic Compounds

chemical nomenclature – the naming of substances
over 10 million known chemical substances

organic compounds – contain carbon

inorganic compounds – everything else

Names and Formulas of Ionic Compounds

positive ions

cations formed from atoms have the same name as the metal
if a metal can form cations of differing charges, the positive charge is given by a roman numeral in parentheses following the name of the metal
cations formed from nonmetal atoms have names that end in –ium

Negative Ions

monatomic anions have names formed by dropping the ending of the name of the element and adding the ending –ide

polyatomic anions containing oxygen have names ending in –ate or –ite

called oxyanions

anions derived by adding H⁺ to an oxyanion are named by adding as a prefix the word hydrogen or dihydrogen, as appropriate

Ionic compounds

names of ionic compounds are the cation name followed by the anion name

Names and formulas of Acids

acids bases on anions whose names end in –ide have associated acids that have the hydro- prefix and an –ic ending
acids based on anions whose names end in –ate or -ite

Anion

Acid

____ide

Hydro____ic acid

____ate

_____ic acid

____ite

_____ous acid

Names and Formulas of Binary Molecular Compounds

the name of the element farthest to the left in the periodic table is usually written first
if elements in same group lower one written first
name of second element is given an –ide ending
greek prefixes used to indicate number of atoms of each element
if prefix ends in a or o and the name of the anion begins with a vowel, the a or o is dropped

Prefix

Meaning

Mono-

1

Di-

2

Tri-

3

Tetra-

4

Penta-

5

Hexa-

6

Hepta-

7

Octa-

8

Nona-

9

Deca-

10

Particle	Charge	Mass (amu)
Proton	Positive	1.0073
Neutron	None	1.0087
Electron	Negative	5.486*10^-4

Anion	Acid
____ide	Hydro____ic acid
____ate	_____ic acid
____ite	_____ous acid

Prefix	Meaning
Mono-	1
Di-	2
Tri-	3
Tetra-	4
Penta-	5
Hexa-	6
Hepta-	7
Octa-	8
Nona-	9
Deca-	10