Chemistry

• Atom


  The basic unit of matter, consisting of a nucleus (protons and neutrons) and electrons orbiting the nucleus.
• Nucleus


  The central part of an atom, composed of protons and neutrons.
• Electron


  Negatively charged subatomic particle that orbits the nucleus in energy levels.
• Proton


  Positively charged subatomic particle found in the nucleus of an atom.
• Neutron

  Neutral (no charge) subatomic particle found in the nucleus of an atom.
• Bohr model

  
  

  A model of the atom proposed by Niels Bohr, in which electrons orbit the nucleus in specific energy levels or shells.
• Energy levels


  Specific regions around the nucleus where electrons are likely to be found in the Bohr model.
• Quantum leap


  The abrupt change of an electron from one energy level to another, as it absorbs or emits a quantum of energy.
• Ground state


  The lowest energy state of an atom, where electrons are in their most stable positions.
• Excited state


  A higher energy state of an atom, achieved when an electron absorbs energy and moves to a higher energy level.
• Electronegativity


  It's a measure of how strongly an atom pulls, attracts, or holds onto electrons in a chemical bond. High electronegativity means the atom is like a magnetic electron-grabber, wanting those electrons close and not willing to share easily.
• Pauling scale


  The Pauling Scale is a way to measure how much an atom loves electrons. A higher Pauling value means an atom is a bit of an electron-hog, pulling electrons closer in a bond. It's like a popularity contest for electrons, and a higher Pauling number means the atom wants to be the center of attention in the electron-sharing party.
• Trend


  The general increase or decrease of electronegativity across a period or down a group in the periodic table.
• High electronegative elements


  Fluorine, Oxygen, Nitrogen, Chlorine
• Least electronegative elements


  Francium, Cesium
• Atomic radius


  The size of an atom, usually measured as the distance from the nucleus to the outermost electrons.
• Trend in atomic radius

  Generally increases down a group and decreases across a period in the periodic table.
• Proton

  Positively charged subatomic particle found in the nucleus of an atom.
• Neutron

  Neutral (no charge) subatomic particle found in the nucleus of an atom.
• Electron


  Negatively charged subatomic particle that orbits the nucleus in energy levels.
• How to calculate electron in an atom

  Electrons are equal to the number of protons in a neutral atom.

  The electron count is the same as the atomic number
• How to calculate protons in an atom

  Protons are identified by the atomic number of an element.
• How to calculate atomic mass

  Atomic mass is the sum of protons and neutrons in an atom.

  Use the atomic mass unit (amu) as the unit of measurement.

  Atomic Mass = Protons + Neutrons.
• Delocalised electrons are removed from metal atoms and therefore can absorb heat and transfer kinetic energy to other delocalised electrons.
• Delocalised electrons have negative charge so they are pushed by the negative electrode and attracted by the positive electrode.
• Metallic bonds are strong so they can withstand high temperatures.
• Not all but the majority of metallic elements in the periodic table can react with acid, water or oxygen.
• Across the periods, ionisation energies of metals increases and therefore their reactivity with acid decreases.
• Elements on the periodic table are numbered in increasing order of the number of protons
• The mass of a proton is approximately the same amount as neutron
• number of neutrons = mass number − proton number
• Isotopes have atoms with a different number of neutrons but the same number of protons.
• Highly electronegative elements will strongly attract electrons.
• Metals are able to easily lose electrons.
• Highly reactive atoms are those that can gain or lose electrons easily.
• Polar covalent bonding: Unequal sharing, partial charges bearing.
• Non-polar covalent bonding: Bonding between atoms with equal electronegativities
• Ionic bonding: Electron transfer from one atom to another, resulting in an ionic compound.