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Element Guide. Atomic Number : number of protons which is equal to the number of electrons. 2. Element Symbol. He. 4. Atomic Mass Number = The number of protons + the number of neutrons. The Periodic Table.

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element guide
Element Guide

Atomic Number: number of protons which is equal to the number of electrons


Element Symbol



Atomic Mass Number = The number of protons + the number of neutrons.

the periodic table
The Periodic Table
  • The periodic table is a bit like a computer keyboard. Just as we combine the letters of the alphabet to make thousands of different words, many of the elements can join in different combinations to make millions of different substances.
  • Groups run vertically in columns in the periodic table.
  • Periods run horizontally.
  • The periodic table gets its name from the fact that patterns occur throughout the table.
  • The metals are most reactive in group I. They become less reactive moving towards the right. They also become more reactive moving down the table from top to bottom.
  • The non-metals are most reactive in group VII. They become less reactive moving towards the left. They also become less reactive moving down the table from top to bottom.
  • The noble gases (group VIII) are left out of this pattern because they do not react (inert).
  • Elements in the same group react in similar ways.


The columns in the periodic table are called groups. Groups of elements share similar reactivity.

This is because they have the same number of valence electrons.

Group 1 are the alkali metals

Group 7 Halogens

Group 8 Noble gases


The rows in the periodic table are called periods.

Atom’s size decreases from left to right in a given period

group 1 alkali metals
Group 1 – Alkali Metals

Group 1 metals are known as the ‘ alkali metals’

  • Group 1 metals include lithium, sodium and potassium..

As you go DOWN Group 1, the alkali metals become more reactive - the valence (outermost) electron is more easily lost, because it’s further from the nucleus and more shielded from it by inner shells.

Group 1 – Alkali Metals

1) The alkali metals all have ONE valence (outer most) electron. This makes them very reactive and gives them all similar properties

2) They all have the following physical properties:

  • Low melting and boiling points (compared with other metals)
  • Low density – Lithium, sodium and potassium float on water
  • Very soft – can be cut with a knife

3) The alkali metals always form ionic compounds.

group 1 reaction with water
Group 1 – Reaction with water
  • When group 1 are put in water, they react vigorously. The reactivity increases down the group – the reaction with potassium gets hot enough to ignite it
  • They move around the surface, fizzing furiously
  • They produce hydrogen
  • Sodium and potassium melt in the heat of the reaction
  • They form a hydroxide in solution, i.e. aqueous OH – ions
  • Na + 2 H2O  2 NaOH + H2
  • Sodium + water  sodium hydroxide + hydrogen
group 7 halogens
Group 7 - Halogens
  • Group 7 is made up of fluorine,chlorine,bromine,iodineand astatine.
  • All group 7 elements have seven electrons in their outer shells (valence electrons) – so they have got similar properties.

As you go DOWN Group 7, the halogens become LESS reactive - there’s less force to pull the extra electron in when it’s further away from the nucleusand more shielding electrons

group 7 halogens1
Group 7 – Halogens


  • Chlorine is a fairly reactive, poisonous, dense green gas
  • Bromine is a dense, poisonous orange liquid
  • Iodine is a dark grey crystalline solid
  • Halogens can either form ionic or covalent compounds
group 7 halogens2
Group 7 – Halogens


Halogens react with alkali metals to form salts

  • They react vigorously with alkali metals to form salts called “metal halides”

2Na + Cl2 2NaCl

2K + Br2 2KBr

More reactive halogen will displace less reactive one

Cl2 + 2KI  2KCl + I2

Cl2 + 2KBr  2KCl + Br2

I2 + KCl No reaction

Br2 + 2KCl  No reaction

diatomic molecules
Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.


The octet rulestates that atoms are most stable when they have a full shell of electrons in the outside electron ring.

  • On the Periodic Chart with shell totals you can easily see the octet rule. A valence is a likely charge on an element ion.

All of the Group 1 elements have one electron in the outside shell and they all have a valence of plus one. Group 1 elements will lose one and only one electron, that single outside electron to become a single positive ion with a full electron shell of eight electrons (an octet)


Group 2 elements all have two electrons in the outer shell and all have a valence of plus two.

  • Group 2 elements lose two electrons to become +2 ions. They do not lose only one electron, but two or none.
  • The Transition Elements, Lanthanides, and Actinides are all metals. Many of them have varying valences. For this reason they sometimes appear to violate the octet rule.

Group 3 elements have a valence of plus three. Boron is a bit of an exception to this because it is so small it tends to bond covalently.

Aluminium has a valence of +3, but some of the larger Group 3 elements have more than one valence.

  • The smallest Group 4 elements, carbon and silicon, are non-metals because the four electrons are difficult to lose the entire four electrons in the outer shell. Small Group 4 elements tend to make only covalent bonds, sharing electrons. Larger Group 4 elements have more than one valence, usually including +4.

Small Group 5 elements, nitrogen and phosphorus, are non-metals. They tend to either gain three electrons to make an octet or bond covalently. The larger Group 5 elements have more metallic character.

  • Small Group 6 elements, oxygen and sulphur, tend to either gain two electrons or bond covalently. The larger Group 6 elements have more metallic character.

Group 7 elements all have seven electrons in the outer shell and either gain one electron to become a -1 ion or they make one covalent bond. The Group 7 elements are diatomic gases due to the strong tendency to bond to each other with a covalent bond.

  • All of the inert elements, the noble gases, have a full octet in the outside shell (or two in the first shell) and so do not naturally combine chemically with other elements.

Electron Configuration

Electrons are are arranged in shells around the nucleus. Each shell is a different energy level.

The first shell fits up to…

The second fits up to…

The third fits up to…

So the electron shell arrangement for 12Mg would be…

2 e

8 e

18 e

2, 8, 2

Interactive periodic table

chemical bonds
Chemical Bonds
  • All atoms want to be like the noble gases.
  • Noble gases have all the electrons they need to fill their ‘outer shell’.
  • Atoms react with other atoms so they can fill their outer shells with the right amount of electrons (we will say that is the magic number 8). This is called covalent bonding where atoms share electrons to achieve their full complement.
  • Ionic bonds are between a metal and non-metal and involves the gain and loss of electrons.
  • When atoms lose or gain electrons, they become ions.
    • ___________ are positive and are formed by elements on the left side of the periodic chart.
    • ____________ are negative and are formed by elements on the right side of the periodic chart.
  • IONS are atoms or groups of atoms with a positive or negative charge.
  • ___________ an electron from an atom gives a CATION with a positive charge
  • __________ an electron to an atom gives an ANION with a negative charge.
  • To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na+ Ca+2 I- O-2

Na Ca I O

ionic bonds
Ionic Bonds

____________ (such as NaCl) are generally formed between metals and nonmetals.

forming cations anions
Forming Cations & Anions

A CATION forms when an atom ______ one or more electrons.

An ANION forms when an atom ______ one or more electrons

F + e- --> ____

Mg ______--> Mg2+

predicting ion charges

In general

  • metals (Mg) _____ electrons ---> cations
  • nonmetals (F) ______ electrons ---> anions
writing formulas
Writing Formulas
  • Because compounds are electrically neutral, one can determine the formula of a compound this way:
    • The charge on the cation becomes the subscript on the anion.
    • The charge on the anion becomes the subscript on the cation.
    • If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.
learning check counting
Learning Check – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+16O -241Ca +2

19 8 20

#p+ ______ ______ _______

#no ______ ______ _______

#e- ______ ______ _______

one last learning check
One Last Learning Check

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 46 e- ___________

charges on common ions






Charges on Common Ions

By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.

  • Atoms have an overall neutral charge because the number of protons ______ the number of electrons.
  • An ion is an atom that has gained or lost one or more electrons.
  • Positive ions are atoms that have _____ electrons.
  • Negative ions are atoms that have ______ electrons.
  • What is the difference between an atom and an ion?
  • List the 3 particles in an atom and their electrical charges.
  • Which particles in an atom determine its atomic number?
  • Explain why the sodium ion carries a positive charge.

Ionic Compounds

The ions that have been formed are now ________ to oppositely charged ions.

So Mg2+ will be attracted to Cl-. This forms an ionic compound.

Some ionic compounds are soluble others are insoluble.

Compounds which are insoluble form solids called precipitates.



So Mg2+ will be attracted to Cl-.

Because Mg is 2+ and Cl is only 1-, Mg will attract 2 Cl’s.

The compound formed will be ______.

The subscript shows that they are 2 Cl’s for each Mg.

If the starting ions were Cu2+ and S2-, the 2 ions have the same charge. So each Cu will only attract 1 S.

The compound formed will be ______.

There is never any charges on the final product - they balance out

covalent compounds
Covalent Compounds

The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.

types of formulas
Types of Formulas
  • Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.
  • Molecular formulas give the exact number of atoms of each element in a compound.
  • Example: glucose C6H12O6
types of formulas1
Types of Formulas
  • Structural formulas show the order in which atoms are bonded.
  • Perspective drawings also show the three-dimensional array of atoms in a compound.
learning check
Learning Check

A. Element in Group XVII, Period 4

1) Br 2) Cl 3) Mn

B. Element in Group II, Period 3

1) beryllium 2) magnesium 3) boron