Feb. 6&7, 2013

Bohr diagrams show how many _____________ appear in each electron shell around an atom.

To begin:

◦ Each shell can hold a certain number of ________________.

◦ The first shell can hold a maximum of _____ electrons.

◦ The second shell can hold a maximum of ________ electrons.

◦ *A BOHR DIAGRAM shows us how many electrons are in each shell surrounding the nucleus.

__________________: is the outermost shell that contains electrons.

__________________: are the electrons in the valence shell.

____________________are involved in chemical bonding.

Electrons can exists as ____________ or in ____________.

The ___________ number determines how many electrons occupy the shells.

Period 1 can hold a maximum of _______ electrons.

Period 2 can occupy _______. If you start left and move right, one more electron is added to the second shell.

When you reach the last element, the shell is called a _________ _________ “Octet” means a complete set of 8.

Elements in period 3 have _______ shells.

(c) McGraw Hill Ryerson 2007

See page 175

The noble gas

elements have full

electron shells

and are very

stable.

(c) McGraw Hill Ryerson 2007

See page 174

What element is this?

•It has 2 + 8 + 8 = 18 electrons, and therefore, 18 protons.

•It has three electron shells, so it is in period 3.

•It has eight electrons in the outer (valence) shell.

18 p

22 n

Let’s try one together:

◦ K, potassium

Please try the following:

H B

Li Ar

Na Mg

F Ne

He Si

P Be

Cl Al

N O

Forming Compounds: ◦ When two atoms move together the valence

electrons interact.

◦ A chemical bond will form if electrons are stable.

◦ Little energy is achieved by having an equal amount of electrons in the valence shell (noble gases).

◦ To get a valence shell like those of noble gases 3 things can happen:

◦ (1)

◦ (2)

◦ (3)

_________________: a pure substance that is composed of 2 or more atoms.

There are two types of compounds

◦ __________________ and __________________

Ionic Bonding:

An ionic compound contains a ___________ ion (usually an metal) and a ______________ ion (usually a non-metal).

In ionic bonding, one or more electrons _________________ from the metal to the non-metal.

LET’S TRY: CaF2 and NaCl

Page 177.

Covalent Bonding:

In ___________________________ atoms will overlap, and one unpaired electron from each atom will pair together.

When non-metals _____________ electrons they form a covalent compound.

A ____________________________________ is a group of atoms in which the atoms are bound together by _______________ one or more pairs of electrons.

Electrons not used in the valence shell are called _______________________.

LET’S TRY: HF, H2O, NH3 and CH4

(c) McGraw Hill Ryerson 2007

Ionic bonds are formed between positive ions and negative ions. ◦ Generally, this is a metal (+) and a non-metal (-) ion. ◦ For example, lithium and oxygen form an ionic bond in

the compound Li2O.

Covalent bonds are formed between two or more non-metals. ◦ Electrons are shared between atoms.

See pages 176 - 177

lithium oxygen

+

Electrons are transferred from the positive ions to negative ions

Li+ O2- Li+

lithium oxide, Li2O

hydrogen fluorine

+

electrons are shared

Hydrogen fluoride

Ionic Bonding:

LiCl, MgO, KF, Li2O and MgCl2

Covalent Bonding:

HF, CH4, H2O, HCL, NH3, and OF2

http://www.youtube.com/watch?v=iih6rJ2S6pk