elements

substances that cannot be broken down into simpler substances by chemical means

essential elements of life

there are 92 natural elements.

96% of the mass of living things is made up of;

• Oxygen

• Carbon

• Hydrogen

• Nitrogen

other elements present in small quantities include Calcium, Phosphorous, Sulfur, Sodium, Chlorine and Magnesium. (remaining 4%)

trace elements:

required by an organism in very small quantities.

(iron, iodine, copper)

where are they found?

• carbon, hydrogen and oxygen are found in all macromolecules

• nitrogen is found in proteins and nucleic acids

• phosphorous is found in nucleic acids and some lipids

Sub-atomic particles

Atom:

smallest unit of an element that retains its characteristic properties.

‘building blocks of the physical world’

• protons

• neutrons

• electrons

protons and neutrons are packed together in the nucleus.

protons are positively charged particles neutrons are uncharged particles.

electrons are negatively charged particles that revolve around the nucleus.

they are considered massless (small size and negligible mass)

most atoms are electrically neutral.

same number of protons and electrons

Isotopes:

atoms that have same number of protons but differ in the number of neutrons in the nucleus.

compounds

when two or more individual elements are combined in a fixed ratio, they form a chemical compound.

a compound has different properties from those of its constituent elements.

atoms of a compound are held together by chemical bonds:

ionic, covalent or hydrogen bonds.

ionic bonds

an ionic bond is formed by the transfer of electrons from one atom to another.

ions:

charged forms of atoms

(two oppositely charged ions form an ionic bond)

covalent bonds

it is formed by sharing of electrons between the combining atoms.

non polar covalent bonds:

when the electrons are shared equally between the combining atoms

polar covalent bonds:

when the electrons are shared unequally due to a small difference in electronegativity.

single double and triple covalent bonds.

water: the versatile molecule

- → polarity → positively charged elements attract the negatively charged ends of other compounds incluuding H2O. Negatively charged ends attract positively charged parts of polar compounds.

→ tendency of water molecules to stick together→ beads and raindrops.

hydrogen bonds

weak chemical bonds that form when a hydrogen atom that is covalently bonded to one electronegative atom is also attracted to another electronegative atom.

they are individually weak but they are strong when present in large numbers.

hydrogen bonds contribute to adhesion, cohesion, surface tension, high heat capacity, expansion on freezing.

why is water a good solvent?

water reacts well with other polar substances.

it can dissolve many kinds of substances.

cohesion & adhesion

they account for the ability of water to rise up roots, trunks and vessels. this is known as capillary action.

cohesion

tendency of water molecules to stick together

adhesion

tendency of water molecules to stick to other substances.

surface tension

caused by cohesion of water molecules.

lets things sit atop/float on the surface without sinking.

high heat capacity

heat capacity:

the amount of heat required to change the temperature of a substance by 1 degree

ie. the ability of a substance to resist a change in its temperature.

waters ability to resist a change in temperature helps keep temperatures in oceans stable helps maintain homeostasis.

expansion on freezing

4 water molecules are bound in a solid lattice of ice, the H bonds cause solid water to expand on freezing.

→ causes ice to become less dense than water.

→ ice floats on water allowing animal life to live underneath the ice

acids and bases

most reactions occur in water based solutions. they are influenced by whether a solution is acidic, basic or neutral.

what makes a solution acidic or basic?

a solution is acidic if it contains a lot of H+ ions.

a solution is basic/alkaline if it releases hydroxide (OH-) ions when added to water.

pH scale

• ranges from 1-14

• 7 is neutral

• 0-7 is acidic

• 7-14 is basic

• blood is around 7.4

organic molecules

organic compounds

chemical compounds within living organisms containing a skeleton of carbon atoms surrounded by hydrogen atoms (and generally some other elements) are referred to as organic compounds.

inorganic compounds don’t contain both carbon and hydrogen atoms.

[it is imperative to have at least one C-C bond present]

carbon: the key element

• tetravalency

• small size

• catenation

• isomerism

polymers

most macromolecules are chains of building blocks known as polymers.

the individual building block of a polymer is known as a monomer.

carbohydrates

monosaccharides

→ linked by glycosidic bonds to form di/polysaccharides.

e.g: glucose, fructose

e.g: glycogen, cellulose, starch

fats/lipids

chains (fatty acids)(saturated of unsaturated) combine on a glycerol backbone to form phospholipids and triglycerides.

they are hydrophobic

cholesterol

proteins

20 different types of amino acids [refer Tbook] with different R-groups link together via a peptide(COHN) bond to form polypeptides.

the chain further folds up into special shapes to make the final protein structure.

1. primary [amino acid sequence]

2. secondary [alpha helixes and beta-pleated sheets]

3. tertiary [disulfide bonds]

4. quaternary [multi polypeptides]

nucleic acids

chains of either DNA (Deoxyribonucleic A) or RNA (ribonucleic acid) nucleotides.

they carry genetic recipes in the body