Chemistry 101

Basic Information

  • Number of protons in the element define the element. Neutrons can change, electrons can change, but if protons change you have a different element.
  • Fundamental elements (or elements with different number of protons in the nucleus) are found in the periodic table
  • Number of protons is the atomic number (Z) of the element
  • Number of neutrons (N) + number of protons (Z) = atomic mass number (A)
  • Isotopes are atoms of the same element which differ in number of neutrons (i.e. they differ in mass). [Image courtesy:]
  • Same number of protons and electrons means it’s neutral. Neutral atom can become +ve or -ve if they depending on shedding or adding electrons.
  • Most of all living things made out of carbon. ~1 million carbon atoms across width of the hair

What are ions?

  • Carbon has 6 protons (and that is what it makes it carbon atom).
  • A neutral carbon atom has 6 protons + 6 electrons. Usually when we use the term atom we refer to neutral atom.
  • The way you get an ion is when you DON’T have the same number of protons and electrons.
  • A carbon atom with 6 protons and 5 electrons is a positive ion (or Cation denoted by C+)
  • A carbon atom with 6 protons and 7 electrons is a negative ion (or Anion denoted by C)

Electron configuration

  • The electron diagrams that we see follow the bohr model which depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar to the structure of the Solar System.
  • It is used to predict reactivity in elements which refers to how likely an element is to form a compound with another element.
  • Valence electrons (the electrons on the last energy level) determine reactivity
  • Rules we follow when laying out the model
    1. Max no. of electrons in a shell given by 2n2, e.g. 2, 8, 16, 32, 50…
    2. Max no. of electrons in the outermost shell is 8
    3. Electrons are not accommodated in a given shell, unless the inner shells are filled.

Ionic bonding

[Images Courtesy:]

  1. Every atom wants a full valance shell!
  2. Sodium gives its one (last) electron (from the valance shell) to chlorine. Now, both valance shells of sodium and chlorine are full.
  3. Sodium now becomes a +ve charged particle while Chlorine becomes a -ve charged particle.
  4. Opposite charges attract, so both these atoms are attracted to each other forming sodium-chloride
  5. Ok, so one of the sodium electrons went to chlorine. Why didn’t the 7 electrons from Chlorine come to sodium?
    Answer is electronegativity. A measure of how badly an atom wants electrons!