The Periodic Table of the Elements
I. Dmitri Mendeleev – he is credited for the creation of the periodic table
II. Element – a pure substance that cannot be broken down into simpler substances.
A. The elements in the periodic table are arranged in order of increasing atomic
number
B. Each box in the table gives the following information:
1. Symbol – one, two, or three letter abbreviation of the elements name
2. Atomic number
3. Mass number
III. Metals, Non-metals, Metalloids – elements to the left of the bold staircase on the
periodic table are metals, while those to the right are non-metals. The
elements on either side of the staircase are metalloids. Note: H is a nonmetal, and Al is a metal.
IV. Monatomic, Diatomic, and Polyatomic Elements – most elements exist as single
atoms; these are called monatomic elements. A few elements are made up
of two elements; these are called diatomic elements (H2, N2, O2,
F2,Cl2,Br2, I2, At2). Two elements are made up of more than 2 atoms – P4,
S8.
V. Physical State of the Elements – All elements are solid under normal laboratory
conditions ( room temperature of 25oC and 1 atm of pressure), except:
a. those that are liquids (Hg and Br2)
b. those that are gases (H2, N2, O2, F2,Cl2, and the Noble gases).
VI. Physical Properties – Metals have luster, non-metals do not have luster (they are
dull). Most metals are malleable (can be rolled or hammered into shape),
ductile (can be drawn into wires), and hard. Non-metals are not malleable,
ductile, or hard.
VII. Sections of the Periodic table
Group or family – vertical columns
Period – horizontal row
Some sections have specific names:
Representative elements – Groups 1-2 and 13-18
Transition elements – Groups 3-12
Alkali metals – Group 1
Alkaline earth metals – Group 2
Noble gases – Group 18
Halogens – Group 17
Inner transition metals – lanthanides
actinides
VIII. Ions- elements gain or lose electrons and become ions. An ion is an atom or group
of atoms that has an electrical charge
A. Cation – an ion that has a positive charge; examples Na+, Mg2+
B. Anion – an ion that has a negative charge; examples Cl-, S2IX. Compounds – When different elements combine chemically, a compound is formed.
There are two types of compounds:
A. Covalent compounds- a compound that is made up of nonmetals
B. Ionic compounds- a compound that is made up of ions.
Usually a metal and a nonmetal. Compounds that contain
NH4+, are also ionic. The metal is written first.
X. Basic repeating units
A. Atoms – an atom is the smallest particle of an element
B. Molecules – a molecule is the smallest particle of a covalent compound or
diatomic/polyatomic element
C. Formula unit – the smallest particle of an ionic compound. F.U. also applies to
element and covalent compounds.
XI. Chemical formulas – A chemical formula gives the elements present in a substance
and the ratios in which they occur. The subscripts represent the number of atoms of
the respective element in one formula unit. Ex. MgCl2 – 1 Mg atom and 2 Cl atoms.
(NH4)2HPO4 – 2 N atoms, 9 H atoms, 1 P atom, and 4 O atoms