Electrons and the Atom SCh3U/4C Ms. Richardson

Refining the Atomic Model Bohr’s work provides information about energy levels at which electrons can exist We can also determine how many electrons exist in each energy level: # electrons in a shell = 2n2 Where n is the number of the shell

Electrons of the Atom When a shell contains the maximum number of electrons, it is said to be filled. Electrons in the outer shell of an atom are known as valence electrons and the shell is the valence shell. The valence electrons are the only electrons involved in forming chemical bonds

Lewis Diagrams and Electrons Lewis diagrams are simplified models used to represent atoms. To draw the Lewis diagram for an atom, we write the chemical symbol and place the valence electrons around the symbol

Lewis Diagrams (continued) Always place electrons at “N, S, E, W” before doubling up.

Lewis Diagrams (continued) Pairing dots when drawing Lewis diagrams for an atom with more than four valence electrons is important. These electron pairs are less likely to participate in bonding than unpaired/lone electrons

The Nucleus Rutherford discovered that the nucleus occupies the centre of the atom as well as many other features of the nucleus

Protons & Neutrons The nucleus is where the mass of the atom is located, comprised of the protons and neutrons.

Neutrons & Isotopes The atomic number represents the number of protons in an atom This also indicates the number of electrons for a neutral atom The number of neutrons in the nucleus of atoms of the same element can vary, as seen with isotopes

Isotopes Isotopes are atoms of the same element that have different number of neutrons This results in a different mass number for the isotope Eg: Carbon-12 and Carbon-14 6 neutrons 8 neutrons

Isotope Notation When representing isotopes, we still use standard atomic notation We can also represent them by naming the element and indicating the mass number Eg: carbon-14, nitrogen-15

Determining Number of Neutrons To find the number of neutrons in an element/isotope, we can use the formula: # of neutrons = atomic mass – atomic number