Chem Chapter 5 - Elements, Compounds And Mixtures

Question 1

What is an element?

Answer 1

A pure substance that cannot be broken down into two or more simpler substances by chemical methods

Question 2

When will elements appear as atoms?

Answer 2

If they are not chemically bonded to each other

Question 3

When will elements appear as molecules?

Answer 3

If they are covalently bonded

Question 4

What are compounds?

Answer 4

A pure substance containing two or more elements that are chemically combined in a fixed ratio

Question 5

What do compounds form when chemically bonded?

Answer 5

Covalent compound or ionic compound

Question 6

Now are compounds separated into their constituents

Answer 6

Chemical methods such as thermal decomposition and electrolysis

Question 7

How does thermal decomposition separate compounds

Answer 7

Exposing the compound to strong heat

Question 8

How does electrolysis separate compounds?

Answer 8

Passing an electric current through the compound

Question 9

What is a mixture

Answer 9

An impure substance containing two Or more compounds and/or elements that are not chemically combined and do not have substances in fixed ratios

Question 10

Name some physical separation techniques that can be used to separate mixtures

Answer 10

Filtration, chromatography and distillation

Question 11

Are new substances formed during separation of mixtures?

Answer 11

No new substances are formed

Question 12

Why do ionic substances have high melting and boiling point

Answer 12

Ions of opposite charges have strong electrostatic forces of attraction between them and a large amount of energy is needed to overcome them. Thus, ionic compounds have high melting and boiling point and are solids at room temperature

Question 13

Why are ionic substances hard?

Answer 13

Strong electrostatic forces of attraction between opposite charged ions make ionic compounds resistant to deforming and resist motion → hard

Question 14

What happens when enough force is applied to an ionic compound?

Answer 14

Ions move away from their lattice positions aud ions of same charge approach each other. Repulsive forces between runs of the same change becomes larger than attractive forces and the lattice structure shatters → brittle

Question 15

Now soluble are ionic compounds?

Answer 15

Soluble in water but are insoluble inorganic solvents

Question 16

Can ionic compounds conduct electricity in the solid state?

Answer 16

When an ionic compound is in the solid state, the ions in the lattice are only able to vibrate about fixed positions which makes ions immobile and cannot conduct electricity

Question 17

Can ionic compounds conduct electricity in the liquid state?

Answer 17

When an ionic compound is molten or in aqueous state, the particles conside pass each other and they are mobile, this they can conduct electricity

Question 18

What are the structural properties of covalent compounds?

Answer 18

Strong covalent bond, molecules held by weak intermolecular forces of attraction and only a small amount of energy is needed to overcome them. Simple covalent substances are usually gases and liquids at room temperature

Question 19

Why do covalent substances have low melting and boiling point?

Answer 19

The weak intermolecular forces of attraction between molecules can be easily overcome with a small amount of energy. Thus making them volatile. As the molecule gets larger, the melting and boiling points are higher. Intermolecular forces of attraction are higher

Question 20

How soluble are covalent substances?

Answer 20

Insoluble in water but soluble in organic solvents

Question 21

Can covalent substances conduct electricity?

Answer 21

No. They do not have any mobile electrons or ions and those electrons are used for bonding and not for sharing and forming ions

Question 22

What is an alloy?

Answer 22

An alloy is a mixture of a metal with one or more other elements

Question 23

Are the number of atoms in an alloy known?

Answer 23

Exact number and distribution unknown, only approximate percentage of each element by its mass is known.

Question 24

What causes alloys to have different properties prom pure metals?

Answer 24

Irregular arrangement of atoms in alloys

Question 25

Have a difference between alloys and pure metals

Answer 25

Harder and stronger than pure metals

Question 26

Name and describe two structural properties of metals and alloys

Answer 26

Malleable: when hammered pure metals can be bent or flattered into a thin sheet
Ductile: pulled (into wire) without breaking
Layer of atoms can slide over one another easily when force is applied

Question 27

Describe the melting and boiling point of metals and alloys

Answer 27

High melting point and boiling point. Solids at room temperature. Alloys do not have a fixed melting point, as they are mixtures that melt over a range of temperatures

Question 28

Are metals and alloys good conductor of heat?

Answer 28

Good conductors of heat

Question 29

Why are metals and alloys good electrical conductors?

Answer 29

Metal atoms have valence electrons freely moving throughout the structure