Diagrams showing the composition of an atom:
◦ number of protons and neutrons in the nucleus
◦ arrangement of electrons in the outer shells
Outermost shell called the valence
Electrons in the valence level are valence electrons
Models include:
◦ Bohr-Rutherford Model
◦ Energy Level Diagrams
Basic Rules for drawing a Bohr-Rutherford
diagram (first 20 elements only):
◦ Draw a circular nucleus
identify the number of protons (P) and neutrons (N)
inside it
◦ Draw circular shells around the nucleus for the
orbiting electrons. For the first 20 elements:
The
The
The
The
first shell can hold 2 electrons.
second shell can hold 8 electrons.
third shell can hold 8 electrons.
fourth shell will hold any remaining electrons.
◦ These rules become more complex for other
elements in the periodic table (more electrons).
Similar to the Bohr Model
◦ instead of drawing circular shells around the
nucleus, lines are drawn above the nucleus
This is an energy level diagram for Neon:
Ions are atoms that have an electrical charge:
◦ Cation – positive charge
◦ Anion – negative charge
The periodic table will usually indicate the most
common ion charge(s) for each element based on
its tendency to gain (-) or lose (+) electrons.
BUT WHY DO ATOMS GAIN OR LOSE ELECTRONS?
To have the same number of electrons as the
nearest noble gas.
◦ The outer energy level wants to be full! This is
done by losing its own valence electrons or by
gaining another atom’s valence electrons.
The first group of elements on the left side of
the table (alkali metals – group 1), each have
a charge of 1+
The halogens (group 17) on the right of the
table have an ion charge of 1-
There are some other general patterns in the
ion charges for each group and each period.
The ion charge is usually written with a plus
or minus sign as a superscript (raised like an
exponent) next to the element.
◦ Ca2+ is a calcium ion with a charge of 2+ meaning it
has lost 2 electrons.
electrons
◦ F 1- is a fluorine ion with a charge of 1- meaning it
has gained 1 electron.
electron
Part 1:
Draw BohrBohr-Rutherford diagrams for elements 110 on the Periodic Table.
Draw Energy Level diagrams for elements 11–20
on the Periodic Table.
Part 2:
Read pages 34–38 (starting with “Formation of
Ions”)
Complete “Check and Reflect” on page 39:
#1 – 3, 5 – 8, 10 – 12
Answer key will be posted on Online Homework