Atoms and Ions

SNC2D

The Bohr-Rutherford Model

Helium Atom • 2 positive protons in nucleus • 2 neutral neutrons in nucleus • 2 negatively charged electrons in the first energy level

Standard Atomic Notation (for a neutral atom)

Atomic symbol Mass number Atomic number 35 80 Br Number of protons Atomic number (35) 35 p + Number of electrons (for neutral atom) Number of neutrons Atomic number (35) Mass number – Atomic number (80-35=45) 35 e 45 n 0

Neutral Atoms and Ions

• When using standard atomic notation you can assume the atom is neutral and the number of electrons is equal to the number of protons • A charge is shown if it is an ion.

35 80 Br 1 – Ionic charge (1 extra electron)

Terms to Know

•

Valence

– The combining capacity of an element •

Valence shell

– The outer electron shell of an atom, the electrons in this shell are called valence electrons •

Isoelectric

with a noble gas – The same number of electrons as a noble gas

The Why of Ions

The Noble Gases do not react and do not form ions because they already have what all atoms want:

f u l l o u t e r s h e l l s

.

Ions

• Many elements want to form stable ions where the number of electrons in the valence shell is the same as a noble gas.

• Metals tend to become positively charged

c a t i o n s

.

• Non-metals tend to become negatively charged

a n i o n s

.

• They become ions by gaining or losing electrons (which ever is easier).

Cations

1+ Na Na

• Easier to lose 1 electron than gain 7. • Therefore the atom becomes a cation by losing an electron.

• It becomes more stable by losing an electron. It becomes iso-electric with Ne.

Anions

1 Cl Cl

• Easier to gain 1 electron than lose 7. • Therefore the atom becomes an anion by gaining an electron.

• It becomes more stable by gaining an electron. It becomes iso-electric with Ar.

Anions

• The elements that form negatively charged ions are

non-metals

.

• Non-metals, when they form ions, change their names to: the first syllable + the suffix “

ide

”

Anion names

chlorine fluorine bromine oxygen sulphur nitrogen phosphorus

Valence Practice

Given the following Bohr diagram, what will the

valence

of the ion be?

1. Na me the following ions: [K] a) Mg 2+ b) O 2 c) Br d) N 3 1. Suppose that a new element has been made. Chemical tests show that it is an alkaline earth metal. [I] a) Predict how many electrons will be in the outer orbit.

b) Predict the ionic charge of the ion that this element forms.

2. Justify why these ions do not exist under normal conditions. [A] a) K 2+ b) O -

Credits

• • http://mr.fusco.ca

http://commons.wikimedia.org/wiki/File:Helium-Bohr.svg