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2.12Chapter 2: Elements, Compounds and Mixtures

What are you made of? — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 12 of 13 1 quiz

📚 Alhussan Chemistry - Stage 7 Hub / Topical Revision
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Lesson summary

2.12 What are you made of?

  • Composition by mass
  • Other elements
  • Trace elements
  • Not mixed up
  • Tissues and organs
  • Proteins, fats and carbohydrates

Part 1 of 7Elements in the human body

Composition by mass
  • Composition by mass oxygen is about 65 per cent, mostly in water, followed by carbon (18 per cent), hydrogen (10 per cent) and nitrogen (3 per cent).
  • These four make up about 96 per cent of body mass.
Other elements
  • Other elements calcium and phosphorus are in bones and teeth.
  • Smaller amounts of sodium, potassium, chlorine, magnesium, sulfur and iron are important.
  • Iron carries oxygen in blood, and sodium and potassium help nerves work.
Trace elements
  • Trace elements zinc and iodine are needed in tiny amounts, but a deficiency causes illness.
Example
  • Example a person of 60 kg with 65 per cent oxygen by mass contains 0.65 × 60 = 39 kg of oxygen.

Part 2 of 7Compounds in the body

Not mixed up
  • Not mixed up the elements are joined in hundreds of different compounds, and are rarely present as pure elements.
Tissues and organs
  • Tissues and organs skin, bones, brain and heart are compounds made mainly of carbon, hydrogen, oxygen and nitrogen.
Blood
  • Blood it is a mixture of compounds, including water, a compound of hydrogen and oxygen.
Keratin
  • Keratin nails and hair are mainly this compound of carbon, hydrogen, oxygen and nitrogen, and sulfur atoms make it hard and rigid.
Vitamins
  • Vitamins they are needed in small amounts and are compounds made mainly of carbon, hydrogen and oxygen.

Part 3 of 7Where body substances come from

1Oxygen
  • Oxygen the air you breathe contains 21% oxygen mixed with other gases, and your lungs separate the oxygen.
2Water
  • Water it comes from food and drink.
3Proteins, fats and carbohydrates
  • Proteins, fats and carbohydrates these compounds are in your food.
4Minerals
  • Minerals you need small amounts of iron and calcium, but swallowing iron nails or lumps of calcium metal would be useless and dangerous.
  • You need compounds that contain these elements, called minerals.

Part 4 of 7Mineral deficiency

MineralSymptoms of deficiency
IronTiredness, lack of energy, shortness of breath
CalciumWeak bones and frequent fractures
ZincReduced growth in children, problems with senses and memory
IodineSwelling of thyroid gland in neck, tiredness, brain damage
  • Iodine in Tanzania
    • in the 1980s about 25% of people had iodine deficiency disorders, so the government told salt makers to add iodine to all salt.
    • In 2004 scientists tested salt from 156 000 households and found iodine added to more than 80% of samples.
    • They tested 166 000 children, and deficiency fell from 25% to 7%.
    • In most areas, the more people ate iodised salt, the fewer had iodine deficiency, so they advised that iodine be added to all salt.

Part 5 of 7Elements in the Earth

Crust
  • Crust it is mostly oxygen and silicon (28 per cent), followed by aluminium, iron, calcium, sodium, potassium and magnesium.
    • (46 per cent by mass)
  • They are combined in compounds such as silicon dioxide (sand and quartz) and silicates.
Atmosphere
  • Atmosphere it is mostly nitrogen (78 per cent) and oxygen (21 per cent), with argon and a little carbon dioxide.
Core
  • Core it is mostly iron and nickel.
PlaceMost abundant elements
Human bodyO, C, H, N
Earth's crustO, Si, Al, Fe
AtmosphereN, O
UniverseH, He

Part 6 of 7Recycling of elements

Atoms are not created or destroyed in chemical reactions,
  • so the elements in your body have cycled through rocks, water, air, plants and animals for millions of years.
Carbon
  • Carbon it moves from carbon dioxide in air into plants by photosynthesis, then into animals that eat plants, and back to air in respiration.
Origin
  • Origin heavier elements were made inside stars that exploded long ago.

Part 7 of 7Extracting and using elements

Ores
  • Ores most metals are obtained from rocks that contain metal compounds.
Methods
  • Methods they depend on reactivity, since very reactive metals like aluminium need electrolysis, whereas iron can be extracted by heating with carbon.
Recycling
  • Recycling resources are limited, which is why recycling is important.

Key terms

TermMeaning
MineralA compound containing an element the body needs, such as iron or calcium.
DeficiencyA lack of something the body needs.
KeratinA compound in hair and nails made of carbon, hydrogen, oxygen, nitrogen and sulfur.
OreA rock containing a metal compound.
Trace elementAn element needed in tiny amounts.
SilicateA compound containing silicon and oxygen found in rocks.

Avoid these mistakes

1
Believing elements in the body exist as pure elements.
2
Thinking the atmosphere is mostly oxygen — it is mostly nitrogen.
3
Saying atoms are used up when we respire.
4
Mixing up the most abundant elements by mass and by number of atoms.

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