Page 348 - General Knowledge

GENERAL KNOWLEDGE 2019

 Elemental Symbol: A1 or 2 letter symbol assigned to each type of atom.
 Elements occur in nature as a mixture. Isotopes are atoms with the same number of protons
but differ in number of neutrons.

Molecular Formula
 The molecular formula identifies which atoms and how many of these atoms will be found in
each molecule.
 The atomic symbol is to identify the atoms and a subscript identifies the number of that
atom.
 is the molecular formula for water.

 Water is composed of hydrogen and oxygen.
 Each water molecule is composed of 2 hydrogen atoms and 1 oxygen atom.
 Since there is only 1 oxygen atom, a 1 will not be written; it is assumed that there is at least
one oxygen, otherwise the O would not have been included in the formula.

 Sulphuric acid has a molecular formula of

 Each molecule is composed of 2 hydrogen atoms, 1 Sulphur atom and 4 oxygen atoms.
Again, since there is only 1 sulphur, the number 1 is not needed as it is assumed.
Energy levels

 Level closest to nucleus is the lowest energy and outer levels have more energy.
st
 1 level – 1 orbital holds 2 electrons
nd
 2 level - 4 orbitals hold 8 electrons
rd
 3 and higher levels – hold increasing numbers of electrons.
 Chemical behavior depends on number of electrons in outermost shell.
 Atoms with the same number of valence electrons have similar chemical behaviors.
 Atom with a completed valence shell = nonreactive.
 Atoms with incomplete valence shells = chemically reactive.
 Atoms can give up, accept, or share electrons in order to have a stable outer shell.

Types of bonds
Covalent
 Single – share a pair of electrons.
 Double – shared two pairs of electrons.
 Triple – shared three pairs of electrons.
 Polar Covalent Bonds: Is seen in atoms with differences in electronegativity one slightly
more positive.
 Non Polar Covalent Bonds: Electron sharing is equally distributed.

Ionic Bonds
 Electrons are transferred from one atom to another (Cation = + Anion = -) +/- partners
(Ions) are held together by attraction between opposite charges.
 Ex: table salt (NaCl) Sodium loses one electron; Chlorine picks up an electron.

Hydrogen Bonds
 The weak attraction between molecules or parts of some molecules.
 It is a slightly positive hydrogen atom of one molecule attracted to slightly negative atom in
another.

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