General chemistry knowledge: Elements Of Life

• Definition of atomic number

  Atomic number = The number of protons
• Definition of mass number

  Mass number = The total number of neutrons + protons
• Definition of isotope 


  Isotope = Atoms with the same number of protons but different number of neutrons
• Definition of Avogadro's Constant

  Avogadro's constant = The number of units in one mole of any substance = 6.02 x10^23
• Definition of relative isotopic mass

  Relative isotopic mass = The mass of an atom isotope compared with 1/12th the mass of an atom of carbon-12
• Definition of relative atomic mass

  Relative atomic mass = The mean weighed mass of an atom of an element compared with 1/12th the mass of an atom of carbon-12
• Definition of relative formula mass

  Relative formula mass = The sum of the mean weighed masses of all atoms in the formula of a compound compared with 1/12th the mass of an atom of carbon-12
• Definition of relative molecular mass

  Relative molecular mass = The mean weighed mass of a molecule compared with 1/12th the mass of an atom of carbon-12
• Properties of a proton

  Relative charge = +1

  Relative mass = 1

  Found in the nucleus
• Properties of neutron 


  Relative charge = 0

  Relative mass = 1

  Found in nucleus
• Properties of electron


  Relative charge = -1

  Relative mass = Very small

  Found in orbit
• What is the electromagnetic spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• AS you go down the electromagnetic spectrum, what happens to the wavelength? 


  Decrease in wavelength
• As you go down the electromagnetic spectrum, what happens to the frequency? 


  Decrease in frequency
• Describe the absorption spectrum

  1. Produced by excited electrons in atom moving between fixed energy levels
  2. If white light is shone through a sample the atoms will absorb certain energies of frequencies AE=hv, causing electrons to be promoted to higher energy levels
  3. The light leaving the sample will be missing these frequencies. These show up as discrete black lines on a coloured background, which converge at higher energy/ frequency
• Describe the emission spectrum

  1. Heating atom, excites the electrons, they are promoted to higher energy levels. They drop back down to lower levels emitting light energy of frequency, given by AE=hv
  2. Each drop gives a discrete line on the emission spectra
  3. It appears as a coloured line on a black background
  4. These lines converge at a higher energy/ frequencies
• What is the shape of the orbitals?

  S - spherical

  p - Infinity
• How many electrons does each sub shell contain?

  S - 1 orbitals can hold 2 electrons

  P - 3 orbitals can hold 6 electrons

  D - 5 orbitals can hold 10 electrons

  F - 7 orbitals can hold 14 electrons

  
• Describe nuclear fusion 


  Nuclear fusion = When 2 lighter nuclei join together to give a new heavier nucleus

  • Occurs in the stars where the is very high temperatures and pressures to overcome the repulsion between two positive nuclei
  • High amounts of energy are released in the process, keeping the star shining
  • The actual nuclei are changing, different elements are given
• Definition of acid 


  Acid = A species that release H+ ions in solution
• Definition of a base

  Base = A soluble alkali
• Definition of an alkali

  Alkali = A species that releases OH- ions in solution
• Definition of neutralisation 


  Neutralisation = When the protons on an acid molecule is replaced by a metal ion forming salt and water
• Name some acids


  • Hydrochloric acid
  • Sulphuric acid
  • Nitric acid
• What is the symbol for hydrochloric acid?

  HCl
• What is the symbol for sulphuric acid?

  H2SO4
• What is the symbol for nitric acid?

  HNO3
• What is the symbol for nitrate?

  NO3-
• What is the symbol for sulphate?

  SO4(2-)
• What is the symbol for carbonate?

  CO3(2-)
• What is the symbol for hydroxide?

  OH-
• What is the symbol for ammonium?

  NH4(+)
• What is the symbol for hydrogen carbonate?

  HCO3(-)
• What is the relationship between metal oxides and alkali?

  Metal oxides and hydroxides are bases. The solution gets more alkali down the group
• What happens when a metal oxide and water react?

  Metal oxides + Water -> Metal hydroxide

  • Oxides react readily with water which dissociates to form hydroxide ions. Metal oxides react slowly and the hydroxide barely dissolves
  • They become more strongly alkaline down the group as the hydroxide becomes more soluble
  • Neutralise acids
• What happens when a metal reacts with water?

  G2 + Water -> Metal hydroxide + Hydrogen

  • Reactivity increases with water down the group
  • Atom gets larger and electrons are further from nucleus
  • Easier to remove and hence more reactive
• What happens as you go down group 2?

  • Increase reactivity
  • Easier to remove e-

  > Weaker attraction

  > Increase shielding

  • e- further from nucleus
  • More shielding
• What is the effect of heat on group 2 metals?

  • More thermally stable as you go down the group
  • More heat to decompose
  • More shells

  > Decrease charge density
• What happens to solubility as you go down group 2? 


  Less soluble

  
• What happens to carbonate as you go down the group?

  • Break down into metal oxides and carbon dioxide via thermal decomposition
  • Less CO2 produces
  • More thermally stable
  • Carbonate ion has a large electron cloud that can be distorted when nearby positive group 2 metal ions
  • As they become larger, the charge spreads over a larger area, therefore a lower charge density

  > Mg2+ has a high charge density and distorts the electron cloud in carbonate ion more than Ba2+ which has a lower charge density. The less distortion the more stable the carbonate is