1.1.1 - Chemistry for life

Question 1

What is a compound?

Answer 1

when an atom of two or more elements react

Question 2

Define ionic bonding.

Answer 2

When an atom donates or receives electrons

Question 3

Define ionic bonds

Answer 3

attractive forces between oppositely charged ions

Question 4

What is a anion?

Answer 4

when an atom gains one or more electrons to become a negative ion.

Question 5

What is a cation?

Answer 5

when an atom loses one or more electrons to become a positive ion.

Question 6

What is covalent bonding?

Answer 6

when the atoms involved in the reaction share electrons

- strong bond

Question 7

what is a polar molecule?

Answer 7

a molecule containing a dipole

Question 8

What is a dipole?

Answer 8

The separation of charge in a slightly polarised molecule

• this is in a covalent compound where the electrons are not evenly shared
• meaning one side is slightly more positive (δ+) /negative (δ-)

Question 9

Name the 4 important anions and what they are needed for.

Answer 9

1. nitrate ions (NO3 -)
   - needed in plants for the formation of amino acids (therefore proteins from the products of photosynthesis)
2. Phosphate ions (PO4 3-)
   - needed in all living organisms for the formation of ATP, ADP, DNA and RNA
3. Chloride ions (Cl-)
   - needed in nerve impulses and many secretory systems
4. Hydrogen carbonate ions (HCO3 -)
   - needed for buffering the blood so it does not become too acidic

Question 10

Name the 4 important cations and what they are needed for.

Answer 10

1. sodium ions (Na +)
   - needed in nerve impulses and many secretory systems
2. calcium ions (Ca 2+)
   - needed for bone formation and muscle contraction in animals
3. Hydrogen ions (H+)
   - needed in cellular respiration and photosynthesis
4. Magnesium ions (Mg 2+)
   - needed for production of chlorophyll in plants

Question 11

Why is water a polar molecule?

Answer 11

• the electrons are held closer to the oxygen atom making it slightly more negative.
• O = δ-
• H2 = δ+

Question 12

Explain why water molecules ‘stick together’.

Answer 12

• refers to the weak electrostatic attraction called a hydrogen bond
• between the slightly negative oxygen atom of one water molecule and the slightly positive hydrogen atom of other water molecules
• causes water molecules to ‘stick together’

Question 13

State the 8 properties of water and briefly explain what they are.

Answer 13

1. is polar solvent - many chemical reactions will occur in water as it is good at dissolving ionic/ covalent substances
2. is an excellent transport medium - because so many substances dissolve in it
3. ice is less dense than water - they are more widely spaced in ice)
4. is slow to absorb and release heat - hydrogen bonds between the molecules means it takes a lot of energy to seperate them (high specific heat capacity)
5. is a liquid - it cannot be compressed
6. the molecules are cohesive - means they stick together
7. the molecules are adhesive - they attract to other molecules
8. has a high surface tension - attraction between water molecules is greater than the attraction between the molecules and the air