Atoms, elements and compounds

Question 1

What is the structure of an atom

Answer 1

a central nucleus containing neutrons and protons surrounded by electrons in shells

Question 2

relative mass of an electron

Answer 2

1/1840

Question 3

What do elements in the same group have in common?

Answer 3

Same number of electrons in the outer shell

Question 4

What do elements in the same period have in common?

Answer 4

The same number of shells

Question 5

What do noble gases have?

Answer 5

A full outer shell

Question 6

Why do isotopes of elements have the same chemical properties?

Answer 6

Isotopes of the same element have the same chemical properties because they have the same number of electrons and therefore the same electronic configuration

Question 7

Describe the giant lattice structure of ionic
compounds

Answer 7

a regular arrangement of
alternating positive and negative ions

Question 8

Properties of ionic compounds

Answer 8

• Usually solid at room temperature
• High melting and boiling points

Ions have a regular arrangement in a lattice structure and they are attracted to each other by strong electrostatic forces of attraction in all directions. Large amounts of energy are needed to overcome and separate ions. The greater the charge on the ions, the stronger the electrostatic forces and the higher the melting point will be.

• Good electrical conductivity when aqueous or molten but poor conductivity when solid

For electrical conductivity to flow there must be free-moving charged particles. Ionic compounds are made of positive and negative ions that are charged. In a solid they can’t move but when in liquid, molten or dissolved they can conduct electricity.

Question 9

How are positive ions formed

Answer 9

Atoms lose electrons from their outer shell when they form positive ions. These ions are positive because they contain more protons than electrons. (Metals are generally cations)

Question 10

How are negative ions formed

Answer 10

A negative ion or anion is an atom that has gained electrons. These ions are negative because they contain more electrons than protons (Non-metals are generally anions)

Question 11

Properties of simple molecular compounds

Answer 11

• Low melting points and boiling points
  Covalent bonds between non-metal atoms are very strong, forming individual molecules. However, these molecules are held together by attractive forces between individual molecules which are very weak (it has weak intermolecular forces)
• Poor electrical conductivity
  Molecular compounds arepoor conductorsof electricity as there are no free ions or electrons to carry the charge. They won’t conduct in any state.

Question 12

Diamond giant covalent structure

Answer 12

Diamond’s structure is an allotrope of carbon where each atom is covalently bonded to 4 other carbon atoms in a tetrahedral arrangement. All the covalent bonds are identical, very strong and there are no intermolecular forces

Question 13

Properties of diamond

Answer 13

• It does not conduct electricity
  All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom, so there are no freely moving charged particles to carry the current thus it cannot conduct electricity
• It has a very high melting point
  The four covalent bonds are very strong and extend in a giant lattice, so a very large amount of heat energy is needed to break the lattice thus it has a very high melting point
• It is extremely hard and dense

Question 14

Use of diamond

Answer 14

• Diamond is used in cutting tools
  The rigid network of carbon atoms, held together by strong covalent bonds, makes diamond very hard.

Question 15

Graphite giant covalent structure

Answer 15

Graphite’s structure is an allotrope of carbon where each atom is covalently bonded to 3 other carbon atoms forming layers of hexagons leaving one free electron per carbon atom that becomes delocalised. The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces meaning graphite has an electrical charge

Question 16

Uses of graphite

Answer 16

• Used as a lubricant

The covalent bonds within the layers are very strong but the layers are connected to each other by weak forces only, hence the layers can slide over each other making graphite slippery and smooth

• Used as an electrode

These free (delocalised) electrons existinbetweenthe layers and are free to move through the structure and carry charge, hence graphite can conduct electricity

Question 17

Properties of graphite

Answer 17

• Conducts electricity
• Has a very high melting point
• Is soft and slippery, less dense than diamond

Question 18

Giant covalent structure of silicon oxide

Answer 18

Each oxygen atom forms covalent bonds with2silicon atoms and each silicon atom in turn forms covalent bonds with4oxygen atoms. A tetrahedron is formed with one silicon atom and four oxygen atoms.

Question 19

Similarities between diamond and silicon (VI) oxide

Answer 19

Both silicon oxide and diamond have tetrahedral structures meaning they both have no delocalised electrons so their properties are similar as they are both hard and have a high melting point. They both also can’t conduct electricity

Question 20

Properties of metals

Answer 20

• High melting and boiling points
  As the electrostatic force of attraction of the metallic bond is strong it requires a lot of energy to overcome resulting in metals being solid at room temp and having high melting and boiling points
• Good electrical conductivity
  There arefreeelectronsavailable to move through the structure and carry charge. Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end. Hence electrons can flow so electricity is conducted
• Malleable and ductile
  Layers of positive ions canslideover one another and take up different positions. Metallic bonding is not disrupted as the outer electrons do not belong to any particular metal atom so the delocalised electrons will move with them. Metallic bonds are thus not broken and as a result metals are strong butflexible. They can be hammered and bent into different shapes or drawn into wires without breaking

Question 21

Law of conservation of mass

Answer 21

During chemical change there is no loss or gain of atoms. The mass of the products in a chemical reaction must equal the mass of the reactants