Atoms, Elements, and the Periodic Table: Summary Notes

Atoms, Elements, and Compounds

  • Atoms: smallest part of an element.

  • Elements: substance with one type of atom, listed on the periodic table.

  • Compounds: two or more elements chemically combined in fixed proportions, with different properties than their constituent elements.

  • Mixtures: two or more elements or compounds not chemically combined; substances retain their properties.

Separating Techniques

  • Filtration: separates insoluble solid from a liquid.

  • Crystallisation/Evaporation: separates a soluble solid from a liquid.

  • Simple Distillation: separates a soluble solid dissolved in a liquid by boiling and condensing the liquid.

  • Fractional Distillation: separates soluble liquids with different boiling points using a fractionating column.

History of Development of the Atom

  • Plum-pudding model: positive charge with negative electrons embedded in it.

  • Nuclear model: mass and positive charge concentrated in the nucleus, with electrons orbiting.

  • Bohr Model: electrons orbit at specific distances (energy levels or shells).

  • Chadwick: discovered neutrons within the nucleus.

The Atom

  • Structure: small nucleus (protons and neutrons) surrounded by electrons.

  • Relative Mass and Charge:

    • Proton: mass 1, charge +1

    • Neutron: mass 1, charge 0

    • Electron: very small mass, charge -1

  • Atomic Number: number of protons.

  • Mass Number: total number of protons and neutrons.

  • Isotopes: atoms of the same element with different numbers of neutrons.

Electronic Structure

  • Electrons occupy specific energy levels.

  • Elements in the same group have similar properties due to the same number of outer electrons.

  • Noble gases are unreactive due to stable electron arrangements.

  • Mendeleev organized early periodic tables, leaving gaps for undiscovered elements.

The Periodic Table

  • Metals form positive ions; non-metals do not (hydrogen is an exception).

  • Metals are on the left/bottom; non-metals on the right/top.

Group 1: The Alkali Metals

  • One electron in the outer shell.

  • Low density, stored under oil.

  • Reactivity increases down the group.

  • React with non-metals to form +1 charged ionic compounds

Noble Gases

  • Unreactive with stable electron arrangements.

  • Boiling points increase with increasing relative atomic mass.

Group 7: The Halogens

  • Seven electrons in the outer shell.

  • Form -1 charged halide ions with metals.

  • Displacement reactions: more reactive halogen displaces a less reactive one

  • Reactivity decreases down the group.

Transition Metals

  • Located between Groups 2 and 3.

  • Higher melting points and densities than Group 1 metals.

  • Less reactive.

  • Form ions with different charges, colored compounds, and act as catalysts.