Chapter 16
Properties of Atoms and the Periodic Table
1. Structure of an Atom
a. Atom – the smallest particle of an element
b. Atoms are made up of three types of smaller particles called subatomic particles;
protons, neutrons, and electrons
i. Protons – particles that contain a positive or a +1 charge.
ii. Neutrons – particles that do not have any charge.
iii. Electrons – particles that have a negative or a -1 charge. They are located in
the space outside of the nucleus.
c. The center of an atom is called the nucleus, which contains both protons and
neutrons.
d. Atomic model – a representation of how the atom looks
i. Democritus – 400 B.C. stated that atoms are particles make up all matter.
ii. Aristotle – Matter was made up of the same material but not of atoms.
iii. John Dalton – 1800, presented his theory on atoms, known as Dalton’s
Atomic Theory.
1. Matter is composed of small particles called atoms.
2. Atoms cannot be destroyed or divided.
3. Atoms of one element are different than those in another element.
4. Atoms can combine in certain amounts to form compounds.
5. In a chemical reaction, atoms are separated, combined or rearranged.
iv. There are three types of models that developed, the Thomson Model,
Rutherford Model, and the Bohr Model.
e. Electron Cloud – the area around the nucleus of an atom where electrons are most
likely to be found.
2. Masses of Atoms
a. The nucleus contains all the weight of an atom. Protons and neutrons are heavier than
an electron.
b. The unit of measurement for an atom’s mass is the atomic mass unit, or amu.
c. Atomic number – the number of protons in an atom’s nucleus.
d. Mass number – the sum of the number of protons and the number of neutrons in the
nucleus of an atom.
e. Isotopes – atoms of the same element that have a different number of neutrons.
f.
Average atomic mass – the weighted average mass of all naturally occurring isotopes
of an element.
3. The Periodic Table
a. The first periodic table was presented in 1800 by Dmitri Mendeleev.
b. In today’s periodic table, elements are arranged by increasing atomic number, and
changes in both physical and chemical properties
c. Periodic table consists of all know elements, and has their name, symbol, atomic
number, and atomic mass
d. Periods – horizontal rows of elements in the periodic table
e. Groups – vertical columns in the periodic table, also known as families.
f.
There are three major groups that elements are classified in, metals, nonmetals, and
metalloids.
Chapter 16 Vocabulary
Atom – the smallest particle of an element that still retains the properties of the element
Atomic Number – number of protons in an atom’s nucleus.
Average Atomic Mass – weighted – average mass of an element’s isotopes according to their natural
abundance.
Electron – particle with the electric charge of -1, surrounds the nucleus of an atom.
Electron Cloud – area around the nucleus of an atom where the atom’s electrons are most likely to be
found.
Group – vertical column in the periodic table.
Isotope – atom of an element that has a specific number of neutrons.
Mass Number – sum of the number of protons and neutrons in an atom’s nucleus.
Neutron – electrically neutral particle inside the nucleus of an atom.
Nucleus – the small, positively charged center of an atom, contains protons and neutrons.
Period – horizontal row in the periodic table
Periodic Table – organized list of all known elements that are arranged by increasing atomic number and
by changes in chemical and physical properties.
Proton – particle in the nucleus with an electric charge of +1.
Quark – particle of matter that makes up protons and neutrons.