1
PERIODIC TABLE OF GROUPS OF ELEMENTS
Elements can be classified using two different schemes.
Metal – Nonmetal Scheme (based on physical properties)
Metals
- most elements are metals
- elements on left side of periodic table are metals
- characteristics of metals
- luster (shine)
- high electrical conductivity
- high heat conductivity (i. e. low specific heats
- ductility – ability of material to be stretched without breaking
- malleability – ability of material to be stamped without breaking
Nonmetals
- elements in the upper right corner of table are nonmetals.
- characteristics of nonmetals
- poor electrical conductivity (insulator)
- poor heat conductivity (insulator)
- all of the gaseous elements are nonmetals
Metalloids
- elements in between metal and nonmetal section of periodic table
- properties of metalloids are in between properties of metals and nonmetals
- moderate electrical conductivity
- as in silicon, which is called a semiconductor since it partially conducts electricity
- only B, Si, Ge, As, Sb, Te, At are metalloids
Group Scheme (based on chemical properties) [Section 4.1]
Alkali metals – column 1A
- first column of periodic table
- Li, Na, K, Rb, Cs, Fr
- all alkali metals may form ions with +1 charge
Alkaline earth metals – column 2A
- second column of periodic table
- Be, Mg, Ca, Sr, Ba, Ra
- all alkaline earth metals may form ions with +2 charge
Transition metals
- middle three rows of table
- Sc to Zn, Y to Cd, La to Hg
- various charges
2
Rare earths
- bottom two rows beside table
- Ce to Lu, Th to Lr
Noble gases – column 8A
- last column of periodic table
- He, Ne, Ar, Kr, Xe, Rn
- essentially unreactive
- also called inert gases
Halogens – column 7A
- second to last column of periodic table
- F, Cl, Br, I, At
- all halogens may form ions with –1 charge
Chalcogens – column 6A
- third to last column of periodic table
- O, S, Se, Te, Po
- all chalcogens may form ions with –2 charge
Pnictogens – column 5A
- fourth to last column of periodic table
- N, P, As, Sb, Bi
- N, P are nonmetals with a -3 charge
- some pnictogens are metalloids (As, Sb)
- Bi is the pnictogen metal (usually +3 charge)
Members of groups have similar physical and chemical properties.
STRUCTURE OF THE ATOM
Atoms have two components.
Nucleus
- all nuclei have positive charge
- contains almost all of the mass of an atom
- >99.95%
- takes up very little volume in atom
Electrons – e- all electrons in the universe are the same
- all have –1 charge
- electron “orbits” around nucleus, orbit takes up most of space
- If nucleus is a penny, then electrons are 75 yards away
- i. e., an atom is mostly empty space!
3
STRUCTURE OF NUCLEUS
Nucleus has two components.
Protons – p+
- all protons in the universe are the same
- all protons have +1 charge
- all positive charge in nucleus comes from protons
- a proton weighs 1 atomic mass unit (amu) (more about this later)
- the number of protons in the nucleus of an atom defines the element of the atom
Neutrons – n0
- all neutrons in the universe are the same
- all neutrons have no charge
-i. e., they are neutral.
- a neutron weighs 1 amu
Atomic Number - Z
- every atom has number which defines its identity, which called its atomic number
*- atomic number is equal to number of protons*
Z = # of p+
Mass Number – A
- every atom has number which approximates how heavy it is, which is called its mass
number
*- mass number is number of protons plus number of neutrons*
A = # of p+ + # of n0
ATOMIC SYMBOLS
Often specific atoms are given a symbol that includes atomic number and mass number.
- Atomic number is written as subscript before elemental symbol.
- Mass number is written as superscript before elemental symbol.
Example: 42 He
2 = atomic number
4 = mass number
Example: An atom has 6 protons and 7 neutrons. Write its chemical symbol.
4
Example: For the atom
37
17
Cl , how many protons neutrons and electrons does it have?
Isotope – Two atoms are isotopes if they have same atomic number but different mass
numbers
- i. e., they have same # p+, but different # n0
- isotopes are the same type of atom, but they have different weights
12
6
C and
13
6
C and
13
6
13
7
C are isotopes
N are not isotopes
IONS AND IONIC COMPOUNDS
Atoms where # e-  # p+ are called ions.
If there are more e-, ion is called an anion.
Ex: Cl- has 17 p+, but 18 eIf there are less e-, ion is called a cation.
Ex: Na+ has 11 p+, but 10 eIons are very common in chemistry.
Anions and cations attract each other to form ionic compounds.
ATOMIC AND MOLECULAR MASSES
Average Atomic Mass
- If element has more than one naturally occurring isotope, atomic mass is an average
of the mass of the isotopes.
- Average is performed accounting for the relative natural abundance of each isotope.
Example: Copper
nuclide
abundance
63
Cu
69.17%
65
Cu
30.83%
mass(amu)
62.940
64.928
Example: Neon
nuclide
20
Ne
21
Ne
22
Ne
mass(amu)
19.992
20.994
21.991
abundance
90.48%
0.27%
9.25%
5
DALTON’S ATOMIC THEORY OF MATTER
1. All matter is made of fundamental building blocks called atoms that are indivisible.
- There is a limit to how small matter can get.
2. Atoms of the same element are identical.
- Very roughly, there are 1050 atoms of hydrogen in the universe and they are all the
same.
3. Chemical compounds are made from whole number of atoms.
- One atom of carbon and one atom of oxygen make carbon monoxide (CO).
- One atom of carbon and two atoms of oxygen make carbon dioxide (CO2).
- We can never put together one atom of carbon and 1½ atoms of oxygen.
- no such thing as ½ atom
4. Chemical reactions are the rearrangement of atoms from one substance to another.
CHEMICAL COMPOUNDS
- three types of chemical compounds
1. Molecular compounds
- tightly bound atoms in a single unit
- binding between atoms is called covalent bonding
2. Ionic compounds
- atoms in compound exist with charges
- such atoms are called ions
- charges on ions attract each other to form chemical compound
- binding between ions is called ionic bonding
3. Intermetallic compounds
- atoms in compound exist without charges
- binding between atoms is called metallic bonding
6
CHEMICAL FORMULAS
- A chemical formula lists all of the elements in a chemical compound.
- Number of atoms of each element is always indicated by subscript after element.
Carbon dioxide – CO2
- one atom of carbon and two atoms of oxygen
Sodium chloride – NaCl
- one atom of sodium and one atom of chlorine
Sucrose – C12H22O11
- 12 atoms of carbon, 22 atoms of hydrogen and 11atoms of oxygen
Note: Some elements exist as molecules rather than atoms.
Gases:
H2, N2, O2, F2, Cl2
Liquid:
Br2
Solid:
I2
Mnemonic: Note these 7 molecular elements look approximately like a 7 on the
periodic table.