Module 2: Water

Question 1

What is water?

Answer 1

Water is a compound of molecules made up of two hydrogen atoms and one oxygen atoms. The hydrogen and oxygen atoms are held together by a covalent bond, which means they share electrons. However, this sharing of electrons is not equal. The oxygen atom has a stronger ‘pull’, resulting in a slight negative charge at oxygen end of a water molecule, and a slight positive charge at the hydrogen end of the molecule. Therefore, water can be described as a polar molecule as it has a positive and negative pole. This results in molecules being attracted to each other (known as hydrogen bonding), which explains many physical properties of water

Question 2

Solids, liquids, and gases

Answer 2

• physical states of matter
• easy to change a substance from one physical state to another
• changes of state results in a change from a solid to a liquid to a gas

Question 3

Particle nature of matter

Answer 3

All matter is made up of small particles

Question 4

Solids:

Answer 4

Strong forces holding particles to one another. These strong forces cause solids to have a definite shape and to be hard, resulting in an orderly arrangement of particles.

Question 5

Liquids:

Answer 5

Particles within a liquid are arranged in a less orderly fashion, and move around more freely. The forces between particles weaker than in solids, and the additional motion results in more kinetic energy.

Question 6

Gas:

Answer 6

The particles within a gas are much further apart than in solids or liquids (very far apart), therefore the particles are moving so rapidly that there no significant forces between them.

• gases can be compressed as there are big spaces between them.

Question 7

Matter

Answer 7

• matter can be either homogenous or heterogenous

- can exist in 3 physical states (solids, liquids, and gases) and two chemical forms (compound or an element)

Question 8

What is heterogenous matter?

Answer 8

Heterogenous matter has a uniform composition and properties. It may exist as a mixture (brass), a compound (water), or an element (pure ion).

Question 9

What is heterogenous matter?

Answer 9

Heterogenous matter does not have a definite composition, such as granite

Question 10

What is a pure substance? Provide examples

Answer 10

A pure substance is homogenous and cannot be separated into 2 or more substances by physical or mechanical means.
A pure substance has a fixed composition, and has constant properties.

Examples - 
Crystals of sugar
Gold 
Copper
Table salt 
Alcohol 
Diamond 
Aluminium

Question 11

What is a mixture? Provide examples

Answer 11

Mixtures can be separated into 2 or more substances by filtering, boiling, or using a magnet. Mixtures may be homogenous (tap water, air) or heterogenous (fruit cake, concrete)
a mixture can be composed of homogenous or heterogenous substances, have variable composition, and may be separated by mechanical (physical) means.

Examples - 
Sea water 
Air
Coffee 
Milk 
Petrol 
Whiskey
Brass
Silver coins

Question 12

What is a compound?

Answer 12

A compound is a pure substance that can be broken down (decomposed) by chemical means. However, a compound can be decomposed into elements.
A compound is made up of two or more elements eg. Salt, water, sodium carbonate, sulfate, alcohol

Question 13

What is an element?

Answer 13

An element is pure substance that cannot be broken down (decomposed) via chemical means.

Question 14

Atoms:

Answer 14

An atom is the smallest particle of an element, which is still recognisable as that element, and are the basic building blocks of matter. They consist of a nucleus and an election cloud.
Each different type of atom contains a certain number of 3 types of subatomic particles: neutrons (no charge), electrons (- charge), and protons (+ charge).

Question 15

A nucleus:

Answer 15

Is composed of protons and neutrons

Question 16

What is a molecule?

Answer 16

Molecules are the second building blocks of matter, and are a combination of two or more of the same or different elements held together by a chemical bond. Molecules are the basic building blocks of many compounds.

Question 17

Atomic bonding - the behaviour of all materials, substances, and matter can be explained in terms of:

Answer 17

The nature of bonding between atoms, and between groups of atoms (know as molecules)

AND

The transfer of energy between the atoms and by the movement of electrons.

Question 18

What are the three types of bonding that are relevant to water molecules?

Answer 18

Covalent bonding
Hydrogen bonding
Ionic bonding

Question 19

How does water form covalent bonds?

Answer 19

Covalency of an atom is the number of electors that an element shares. Covalent bonds occurs between two non- metals.
Hydrogen has a covalency of 1 - so it will share 1 electron
Oxygen atom has a covalency of 2 - so will share two electrons

Question 20

Sharing electrons in covalent bonds:

Answer 20

The electrons in a covalent bond are shared.

A pair of electrons are shared equally with two identical atoms

Question 21

Unequal sharing of electrons:

Answer 21

a covalent bond between different atoms has an unequal sharing of electrons.
- when oxygen and hydrogen share electrons, the electrons are more closely associated with the oxygen atom, resulting in a slight negative charge forming on the end of the oxygen atom, and a slight positive charge forming on the end of the hydrogen atoms

Question 22

Shape and charge of a water molecule

Answer 22

Water is not linear. The angle between the hydrogen atoms is 104.5* therefore one end of water will have a slightly positive charge and the other will have a slightly negative change l - making it a polar molecule because it has a positive and negative pole

Question 23

What is hydrogen bonding?

Miller & Spoolman, 2013

Answer 23

When water molecules approach one another, they will form hydrogen bonds between the slightly positive hydrogen atom or one water molecule and the slightly negative oxygen of another molecule.

Question 24

Hydrogen bonds

Answer 24

The strongest type of intermolecular bond. The small size of the water molecule compared to the magnitude of the hydrogen bonding attraction results in many of water’s physical properties. The presence of hydrogen bonding results in many of water’s chemical properties

Question 25

Sodium chloride - ionic bonds

Answer 25

• Many elements have an electrovalency.
• Similar to a covalency, but refers to the tendency to lose or gain electrons - NOT share
• tend to form between a metal and a non- metal

Question 26

Structure of ionic compounds

Answer 26

Consist of orderly arrays of positive and negative ions

Question 27

Ionic compounds and water

Answer 27

Sodium chloride, and many other ionic compounds tend not to dissolve in water and break apart unit their individual ions.

Question 28

What are the chemical and physical properties of water?

Answer 28

• relatively high boiling point
• Will dissolve ionic compounds and sugars
• is not miscible with carbon based compounds like oils
• ice floats on water
• high surface tension

Question 29

What is the kinetic theory and nature of matter?

Answer 29

The behaviour of substances in solid, liquid, and gas stages can be explained in terms of kinetic theory and the particular nature of matter

Question 30

What is the kinetic theory?

Answer 30

The kinetic theory explains the nature of matter. The Kinetic energy assumes that all materials that surround us in our everyday lives are made up of a variety of substances. These substances are made up of collections of particles. According to the kinetic theory, the very small particles (that maybe atoms of an element or molecules of a compound) are in constant motion