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2.4Chapter 2: Elements, Compounds and Mixtures

Atoms — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 13 2 quizzes

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

2.4 Atoms — Elements and Atomic Arrangement — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define atom and element, describe how atoms are arranged in elements, and explain that the properties of an element are the properties of many atoms together.Atom = the sm…

  • Own type of atom
  • Limitations
  • Single atoms
  • Giant structures
  • Allotropes
  • Reading a diagram

Section 1 of 9Atoms

Atom
Atom the smallest particle of an element that can exist.
Size
  • Size the diameter of one atom is about 0.000 000 01 cm, so one hundred million atoms side by side stretch one centimetre.
Pictures
  • Pictures a special microscope can show the surface of silicon magnified ten million times, and the spheres in it are atoms.

Section 2 of 9Atoms and elements

Atoms and elements
Own type of atom
  • Own type of atom every element has its own type of atom,
  • so all silicon atoms are alike, all platinum atoms are alike and the atoms of each element differ from those of every other element.
  • Atoms of different elements differ in mass and in the number of protons.
  • There are about 100 elements, so there are about 100 types of atom.
Element
Element a substance that is made from one type of atom and cannot be split into other substances.
Silicon
  • Silicon it is the main element in a lump of silicon and in the integrated circuits in electronic devices,
    • where its semiconductor properties are useful.

Section 3 of 9Properties of an element

Many atoms
  • Many atoms the properties of an element are the properties of many atoms together.
  • A block of copper of 1 kg contains about 9 000 000 000 000 000 000 000 000 atoms, which together make copper red-brown and shiny.
  • A single copper atom is not red-brown or shiny and is not in a solid, liquid or gas state.
Melting
  • Melting in the block the atoms have fixed positions, and at 1084 °C they leave their positions and slide over each other.
  • One atom cannot melt, and only many atoms together can.

Section 4 of 9Modelling atoms with toy bricks

Strengths
  • Strengths the model shows that every element has its own type of atom and that many atoms may join together.
  • Bricks of one colour represent atoms of one element, such as gold, oxygen or nitrogen.
Limitations
  • Limitations atoms do not have straight edges and are much smaller than toy bricks.

Section 5 of 9Arrangements of atoms in elements

Arrangements of atoms in elements
Single atoms
  • Single atoms the noble gases such as helium and neon exist as separate atoms because their atoms are stable on their own.
Molecules
  • Molecules some non-metal elements have atoms joined together.
  • Hydrogen (H2), oxygen (O2), nitrogen (N2) and chlorine (Cl2) have two atoms per molecule.
  • Sulfur forms S8 rings and phosphorus forms P4.
  • Weak forces between molecules give these elements low melting and boiling points.
Giant structures
  • Giant structures in metals atoms are packed in regular layers, which explains why metals can be bent and hammered and conduct electricity.
  • In diamond and graphite millions of carbon atoms are joined in a giant network.

Section 6 of 9Allotropes

Allotropes
Allotropes different structures of the same element.
Carbon
  • Carbon diamond and graphite are both pure carbon, but the atoms are arranged differently.
  • Diamond is very hard, each carbon atom joined to four others in a strong three-dimensional network, with a very high melting point.
  • Graphite is soft and conducts electricity.

Section 7 of 9Particle diagrams

DiagramMeaning
All identical single circlesElement made of single atoms (for example neon)
Identical pairs of joined circlesElement in molecules (for example O2)
Different joined circlesCompound
Different separate circlesMixture
  • Reading a diagram
    • count the types of circle first, then check whether they are joined or apart.

Section 8 of 9Key terms

TermMeaning
AtomThe smallest particle of an element that can exist.
ElementA substance made from one type of atom.
MoleculeTwo or more atoms joined together.
AllotropeA different structural form of the same element.
ModelAn idea that explains observations and helps make predictions.
SemiconductorA material, such as silicon, that conducts electricity only partly.

Section 9 of 9Exam technique

1
Saying a molecule of an element is a compound.
2
Thinking atoms of the same element can be different elements.
3
Saying an element must be single atoms.
4
Believing all atoms are the same size.

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