L3 - Atoms & Ions
Unit 2: Meet the Elements
Atom interactions are shown by chemical formulae, which in turn can be
used to identify relationships between classes of chemicals, predict reaction
outcomes, and balance equations.
Key Concept: Relationships, Related Concepts: Balance, Interaction
Learning Targets
● Define the terms cation and anion.
● State the differences between an atom and
an ion.
● State the octet rule.
Atoms - Recall
Atoms are a unit of matter.
They are the smallest unit of an element that
retains all the properties of its element.
An atom has fixed number of protons. The
atomic number on the Periodic Table tells you
the # (number) of protons in an atom of that
element.
An Atom is electrically neutral. The number of
protons (+) is equal to the number of electrons
(-).
Valence Shell
(or Outer Orbital) - is special!
An atom’s electrons are
found in orbitals outside of
the nucleus.
The outer orbital or ‘shell’
is the place where an atom
will gain or lose electrons.
The valence electrons
determine how the atom
behaves in chemical
reactions
Look at the pictureWhat element is this?
How do you know?
Noble Gases have 100% filled
orbitals and are thus
unreactive
Remember: 2, 8, 8, 2
Related Concept: Balance
Families / Groups have the
same # of valence electrons
in their outer shell
Key Concept: Relationships,
Related Concept: Balance
2, 8, 8, 2
The ‘stable octet’ rule
Octet Rule
● The Octet Rule states that
elements gain or lose
electrons to attain an electron
configuration of the nearest
noble gas.
● Atoms follow the octet rule
because they always seek
the most stable electron
configuration.
● The Octet Rule is used
exclusively to describe the
electron configurations of the
first 20 elements.
Octet Rule- limits how many electrons
can go into each orbital
State the element’s name
What is its atomic number?
How many protons are there
in its nucleus?
Do the number of electrons
equal the number of protons?
Related Concept: Balance
Does the distribution of the
electrons follow the octet rule
of 2, 8, 8, 2?
Octet Rule- limits how many electrons
can go into each orbital
State the element’s nameSulphur
What is its atomic number?16
How many protons are there
16
in its nucleus?
Do the number of electrons yes
equal the number of protons?
Related Concept: Balance
Does the distribution of the
electrons follow the octet rule
of 2, 8, 8, 2? yes
Forming Cations
To form positive ions electrons are lost.
Positive ions are called cations.
To form negative ions electrons are gained.
Negative ions are called anions.
Simulator
An extra resource if you’d like to give it a try.
Atoms to ions
Name
Lithium (Li)
Oxygen (O)
Chlorine
(Cl)
Aluminium
(Al)
Magnesium
(Mg)
Atomic
number
3
Electron
arrangement
Needs to
lose or gain
electrons?
2,1
Lose 1
Ion formed
Li +
Atoms to ions
Name
Atomic
number
Electron
arrangement
Needs to
lose or gain
electrons?
Ion formed
Lithium (Li)
3
2,1
Lose 1
Li +
Oxygen (O)
8
2,6
Gain 2
O2-
Chlorine
(Cl)
17
2,8,7
Gain 1
Cl-
Aluminium
(Al)
13
2,8,3
Loses 3
Al3+
Magnesium
(Mg)
12
2,8,2
Loses 2
Mg2+
Ions
What is the relationship
between atoms and ions?
An ion is an atom that has gained
or lost electrons.
A cation - is an atom that has
lost electrons and has excess
positive charge around it.
An anion- is an atom that has
gained electrons and has excess
negative charge.
Losing/Gaining electrons
In the examples below, is it easier for them to gain or
lose electrons? Justify your answer
Atoms to Ions
Metal Atoms LOSE their
valence electrons to leave
a full outer shell.
The excess charge
(gained or lost) is written in
superscript next to the
atom symbol. Two ways
are shown in the pictures
of how to do this.
Nonmetal Atoms GAIN
electrons to fill their
valence shell until full
(stable).
Summary of what we have covered so far- watch
the video in Presentation Mode- scroll over box to show play button.
Quiz
Review
Periodic table information
http://www.chem4kids.com/extras/quiz_elempertable/
(the above website also provides you with short sentences for more information on
the answers)
How to figure the number of protons. neutrons, electrons and mass number
http://education.jlab.org/elementmath/
Elements, Compound and Mixtures
http://www.syvum.com/cgi/online/mult.cgi/squizzes/chem/elements_compounds_mixt
ures.tdf?0
Balancing Equations Simulation
https://phet.colorado.edu/sims/html/balancing-chemical-equations/latest/balancingchemical-equations_en.html