PERIODIC TABLE OF GROUPS OF ELEMENTS Elements can be classified using two different schemes.

PERIODIC TABLE OF GROUPS OF ELEMENTS

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

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

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!

STRUCTURE OF NUCLEUS

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: ₂⁴H e

2 = atomic number 4 = mass number

Example: An atom has 6 protons and 7 neutrons. Write its chemical symbol.

Example: For the atom ₁₇³⁷C l , 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

6

1 2

C

C

6

1 3

C

N

IONS AND IONIC COMPOUNDS

If there are more e^-, ion is called an anion.

Ex: Cl^- has 17 p⁺, but 18 e^-

If there are less e^-, ion is called a cation.

Ex: Na⁺ has 11 p⁺, but 10 e^- Ions are very common in chemistry.

Anions and cations attract each other to form ionic compounds.

ATOMIC AND MOLECULAR MASSES

- 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 mass(amu)

63Cu 69.17% 62.940

65Cu 30.83% 64.928

Example: Neon

nuclide abundance mass(amu)

20Ne 90.48% 19.992

21Ne 0.27% 20.994

22Ne 9.25% 21.991

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

- 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

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.