2.1 Chemical Bonds, Ionic, Covalent & Metallic

What are the three types of strong chemical bonds?

• Ionic

• Covalent

• Metallic

For ionic bonding the particles are ________________ ___________ _______.

oppositely charged ions

For covalent bonding the particles are atoms which __________ ________ of ____________.

• share

• pairs

• electrons

For metallic bonding the particles are atoms which _________ _________________ ____________.

• share

• delocalised

• electrons

What does ionic bonding occur in?

Compounds formed from metals combined with non-metals.

What does covalent bonding occur in?

• Most non-metallic elements

• Compounds of non-metals

What does metallic bonding occur in?

• Metallic elements

• Alloys

What is a compound?

A substance which contains two or more elements chemically combined in fixed proportions.

When an atom loses electrons it becomes a ____________ ion.

positive

When an atom gains electrons it becomes a ____________ ion.

negative

What is the process of ionic bonding?

• A metal atom reactions with a non-metal atom — electrons from outer shell of metal atom are transferred.

  • metal atoms lose electrons → positively charged ions

  • non-metal atoms gain electrons → negatively charged ions

• The ions produced have a stable electronic structure (like that of a noble gas).

What type of bonding does sodium chloride have? Describe it.

• Ionic bonding

• The outer shell electron on the sodium atom is transferred to the chlorine atom.

  • The sodium atom has lost an electron → positively charged ion

  • The chlorine atom has gained an electron → negatively charged ion

• Both of these ions have the stable electronic structure of a noble gas.

What is an ionic compound?

A giant structure of ions.

What are ionic compounds held together by?

Strong electrostatic forces of attraction between oppositely charged ions.

• Ionic compounds are held together by strong ____________ forces of _____________ between _____________ __________ ______.

• These forces act in ____ __________ in the _________ — this is called ______ __________.

• electrostatic

• attraction

• oppositely charged ions

• all directions

• lattice

• ionic bonding

What are the limitations of using dot and cross diagrams to represent ionic compounds?

• Useful for showing how electrons are transferred

• Doesn’t show the 3D arrangement of the ions in space

What are the limitations of using 2D diagrams to represent ionic compounds?

• Clearly shows how ions are arranged in one single layer

• Doesn’t show how the next layers of ions are arranged behind or in front of it

What are the limitations of using 3D ball and stick models to represent ionic compounds?

• Shows the 3D arrangement of a larger section

• Misleading — uses physical ‘sticks’ for bonds

  • There are no solid sticks of gaps between ions — strong electrostatic forces of attraction acting in all directions

What are the limitations of using 3D space-filling models to represent ionic compounds?

Misleading if they show lots of free space between individual ions — doesn’t exist in a tightly packed lattice

• Figure 3 represents the structure of manganese oxide.

• Manganese oxide is an ionic compound.

Determine the empirical formula of manganese oxide. [1 mark]

Use Figure 3.

MnO

What bonds are formed when atoms share pairs of electrons?

Covalent bonds

What may covalently bonded substances consist of?

Small molecules

• Some covalently bonded substances have very large molecules, such as __________.

• Some covalently bonded substances have giant covalent structures, such as __________ and _________ ___________.

• polymers

• diamond

• silicon dioxide

What are the limitations of using dot and cross diagrams to represent molecules of giant structures?

• Clearly shows pairs of outer electrons and which atoms they came from

• Doesn’t show the 3D shape of how atoms are arranged in space

What are the limitations of using 2D structural formulas to represent molecules of giant structures?

• Shows which atoms are connected by bonds

• Doesn’t show the 3D structure and which atoms the electrons came from

What are the limitations of using 3D ball and stick models to represent molecules of giant structures?

• Shows the 3D arrangement of atoms in space

• Misleading — uses physical ‘sticks’ for bonds

• Propanone is a compound of carbon, hydrogen and oxygen.

• Figure 1 shows the dot and cross for a propanone molecule.

Determine the molecular formula of propanone. [1 mark]

Use Figure 1.

C₃H₆O

• This question is about citric acid.

• Figure 1 represents one molecule of citric acid.

Complete the molecular formula of citric acid. [1 mark]

C₆H_{__}O_{__}

Use Figure 1.

• 8

• 7

What do metals consist of?

Giant structures of atoms arranged in a regular pattern.

• The electrons in the outer shell of metal atoms are ________________ and so are free to move through the whole ____________.

• The __________ of ____________ electrons gives rise to strong ____________ bonds.

• delocalised

• structure

• sharing

• delocalised

• metallic

• The table shows the structures of three compounds.

Compare the structure and bonding of the three compounds:

• carbon dioxide

• magnesium oxide

• silicon dioxide

[6 marks]

• Both carbon dioxide and silicon dioxide are made up of atoms — but magnesium oxide is made up of ions.

• Both silicon dioxide and magnesium oxide are giant structures — but carbon dioxide is small molecules with weak intermolecular forces.

• All three compounds have strong bonds.

• Both carbon dioxide and silicon dioxide are formed from two non-metals

  • so the bonds formed are covalent

  • so the electron pairs are shared between atoms

• But magnesium oxide is formed from a metal and a non-metal

  • so the bonds in magnesium oxide are ionic

  • so electrons are transferred from magnesium to oxygen — two electrons are transferred