Ionic Bonding - Metal Compounds

Comparing the electron arrangements of the first 20 elements

Elements in the same Vertical Group have electron arrangements with the same number of electrons in the

outer shell. (energy level)

The number of electrons in the outer shell (energy level) is the same number as the Group number; ie.

Elements in Group II have 2 electrons in their outer shells; (energy levels) Elements in Group V have 5

electrons in their outer shells. (energy levels)

When atoms react, it is their outer parts (their outer electron shells or energy levels) which collide. Atoms with

the same number of electrons in their outer shells (energy levels) show similar chemical reactions because of

this.

The "Noble" or "Inert" gases, Group VIII, are highly stable elements and have highly unreactive atoms. This is

because their atoms have a FULL outer electron shell. (energy level)

Elements react with other elements so as to try to become unreactive. It is the outermost electron shells

(energy levels) of atoms that interact when atoms collide and react. Atoms try to gain a full outer shell (energy

level) of electrons, similar to that of the nearest Inert Gas, by losing or gaining electrons.

Look at the elements SODIUM and CHLORINE.

Ionic Bonding - Sodium Chloride

SODIUM and CHLORINE react together to form a white crystalline solid called SODIUM CHLORIDE. Sodium

chloride has a very high melting point, 8080C, conducts electricity when it is molten and dissolves in water to form a

solution that also conducts electricity. The solid sodium chloride does not conduct electricity. This being the case,

the electrical conductivity of sodium chloride cannot be due to "free" electrons that roam throughout the structure

between the atoms as what happens in metals. Its conductivity in liquid or solution forms and non-conductivity in

solid form must be due to the fact that when molten or liquid, the particles that make up sodium chloride must be

able to move whereas they were in fixed positions when solid and so could not move.

To better understand the structure and bonding in sodium chloride, we will have to take a closer look at the

electron configuration or structure of their atoms.

Na has 1 electron in the outer shell MORE than a noble gas (NEON 2.8) whereas Cl has 1 LESS than a noble gas

(ARGON 2.8.8).

When atoms react, they try to lose or gain electrons in their outer energy shell in order to get their outer shell

FULL. If an atom has 1, 2 or 3 electrons in their outer energy shell, they try to LOSE these electrons to the atoms 1

they wish to react with. This particular outer energy shell disappears, leaving the next electron shell as the outer

shell and this shell is FULL.

METALS react in this way because metals are located in Groups I, II, or III in the Periodic Table and contain 1, 2 or

3 electrons in their outer energy shell.

SODIUM can react and become stable by losing 1 electron from its outer energy shell. This energy shell

disappears and the next one that contains 8 electrons becomes a FULL OUTER ENERGY SHELL.

CHLORINE can react and become stable by either LOSING 7 OUTER ENERGY SHELL ELECTRONS or by

GAINING 1 ELECTRON into its outer energy shell. This now becomes full containing 8 electrons. It is obviously

far easier to gain 1 electron than to lose 7. If an atom has 7, 6 or 5 electrons in its outer energy shell, it gains a full

outer energy shell by GAINING electrons.

NON-METALS react in this way because non-metals are located in Groups V, VI and VII in the Periodic Table and

contain 5, 6 or 7 electrons in their outer energy shell and so are 3, 2 or 1 electron short of a full shell.

METALS LOSE ELECTRONS TO NON-METALS, WHICH GAIN THEM.

Sodium + Chlorine Sodium Chloride

2 Na + Cl2 2 NaCl ( Na+ Cl− )

Calcium Sulphide

Formula = CaS

Calcium + Sulphur Calcium Sulphide

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11 protons and only 10 electrons (a 1+ ION)

One SODIUM atom is required to lose an electron to one CHLORINE atom, which gains it.

17 protons but 18 electrons (a 1− ION)

Ca + S CaS ( Ca2+ S2-)Magnesium Fluoride

Now we will look at what happens when a metal atom with TWO electrons in its outer energy level combines with a

non-metal with 7 electrons in its outer energy level.

Magnesium atoms are 2.8.2 and become magnesium ions, 2.8.

Fluorine atoms are 2.7 and become Fluoride ions, 2.8.

Formula = MgF2

Magnesium + Fluorine Magnesium Fluoride

Mg + F2 MgF2 ( Mg2+ (F-)2 )

Now draw electron energy shell (dot and cross) diagrams to show the formation of LITHIUM OXIDE and

MAGNESIUM SULPHIDE.

Other compounds to do: -

LITHIUM FLUORIDE; POTASSIUM FLUORIDE; SODIUM SULPHIDE; CALCIUM OXIDE;

MAGNESIUM CHLORIDE; MAGNESIUM OXIDE; ALUMINIUM FLUORIDE.

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Magnesium needs to lose 2 electrons. Since Fluorine has only one space for an electron in its outer level, TWO Fluorine atoms are needed. The formula is

MgF2 and contains

Magnesium ions, Mg2+

and

Fluoride ions, F−.

Ionic Bonding - Metal Compounds

Write the title. Read the information sheet on “Ionic Bonding – Metal Compounds and then answer the questions.

Questions write out the following questions/statements and complete them.

1. The Noble Gases are unreactive because they have a full shell of eight electrons and so they do not need

to lose or gain any.

2. The Group 1 elements called the alkali metals, such as sodium (complete) have all got one electron in their

outer shells. In order to achieve the electron configuration of the nearest Noble gas, they have to lose

(lose/gain) one electron.

3. The Group 7 elements, called halogens, such as chlorine (complete) have all got seven electrons in their

outer shells. In order to achieve the electron configuration of the nearest Noble gas, they have to gain

(lose/gain) one electron.

4. Draw the dot and cross diagrams to show SODIUM reacting with CHLORINE to form SODIUM

CHLORIDE.

5. Underneath each electron shell diagram, show the electron configuration of each atom and each ion (in the

form of 2.8.1 for example)

6. Write a balanced symbol equation for the reaction between Na and Cl2.

2Na + Cl2 -> 2NaCl

7. Answer Q4 to 6 for the compounds listed at the bottom of page 3 of the information sheet.

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Figure 1: Ionic lattice - NaCl

Covalent Bonding – Non – metal Compounds

This type of bonding is found when non-metal elements combine with other non-metal elements to form non-metal

compounds. Non-metal elements want to GAIN electrons because they have 1, 2 or at most 3 electrons LESS in

their outer energy levels than a full level. When combining with metal atoms, they gain these electrons from the

metal atoms. When atoms of two non-metal elements combine, atoms of BOTH elements wish to GAIN electrons.

In order to overcome this problem, the atoms of the two elements involved in bonding SHARE the number of

electrons each requires to gain a full level.

eg HydrogenEach Hydrogen atom requires one more electron in order to

complete its outer shell. Therefore it has to be prepared to share

one of its own. Both Hydrogen atoms share their only electron and

overlap their electron shells so that their only electron belongs to

both outer shells of both atoms.

The pair of electrons is called a COVALENT BOND and attracts the

nuclei of both individual atoms in the molecule together by

electrostatic forces of attraction. However, unlike in the case with ions in metal compounds which attract other

oppositely charged ions around them in all directions, the forces of attraction from the covalent bond pair of

electrons does not spread out beyond the molecule and so, although the atoms within the molecule are held

together by strong forces, molecules attract other molecules with only weak forces.

Hydrogen is a GAS.

Methane, Carbon Hydride.

CARBON atoms have 4 electrons in their outer levels. They need to gain 4 more electrons to get a full outer level

and so must SHARE 4 of its own. Hydrogen has one electron in its outer level and also needs to GAIN electrons,

but only one.

The outer shells of 4 Hydrogen atoms overlap with the outer shell of the Carbon atom. Each Hydrogen provides

the Carbon atom with one electron, so all 4 Hydrogen atoms will provide Carbon with the 4 electrons that it needs.

In exchange, the carbon atom shares one of its electrons with each of the four Hydrogen atoms so that they, too,

now have a full outer level of 2 electrons.

One Hydrogen atom shown bonding to the Carbon atom

with its electron and one of Carbon's outer shell

electrons now in the outer the shells of BOTH Carbon

AND Hydrogen.5

All four Hydrogen atoms shown bonded to

Carbon in METHANE, CH4 .

The atoms are held together by the electrostatic force of attraction between the electrons that are being "SHARED"

and the positively charged nucleuses of the two bonding atoms.

This bond is called an "ELECTRON PAIR COVALENT BOND".

We can draw simpler electron diagrams showing this type of bonding without drawing all the electrons. We just

consider only the OUTER energy level electrons and assume that the inner levels are there and full, but we do not

draw them.

We draw the electrons of one atom as DOTS and those of the other atom as CROSSES.

Each dot and cross electron pair is a COVALENT

BOND.

Draw electron level diagrams for the following compounds. Predict their formulas, draw dot and cross diagrams as

well as atom and stick bond diagrams.

Hydrogen Chloride

Ammonia (Nitrogen Hydride)

Water

Carbon Dioxide

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Hydrogen Chloride

Water

Ammonia

Carbon Dioxide

The element gases, Hydrogen, Chlorine, Oxygen and Nitrogen

Individual atoms are highly reactive because they do not have a "FULL OUTER

ENERGY LEVEL". For this reason, TWO atoms join together, sharing

electrons in order to enable each other to have full outer energy levels. For

this reason, these element gases are DIATOMIC. (molecules containing TWO

atoms).

Other molecules to consider are Ethane and Ethene.

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Formula O2

Formula H2

Formula Cl2

Formula N2