CHEM 1406 Concept Review: Atoms and Elements

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Periodic Table:  A table that arranges all known elements in order of atomic number and in a way that groups together elements that have similar properties.

Period: A row in the periodic table. 

Group:  A column in the periodic table.  Elements in the same group tend to have similar properties.  Certain groups have special names that are often derived from the specific chemical properties of elements in the group.

 

Representative elements:  Elements that are labeled with an “A” and are sometimes simply called “A-group elements”.  These are called “representative” because they represent the broad spectrum of physical and chemical properties present among the many elements in the periodic table.

Metals:  Elements that tend to be shiny, malleable (able to be hammered into sheets), ductile (able to be drawn or “pulled” into wires), and conduct heat and electricity well.

Nonmetals:  Elements that tend to be dull, brittle, and do not conduct heat or electricity well as solids or liquids.  Most non-metals are in the gas phase at normal temperatures.

 

 

Precepts of Dalton’s Atomic Theory

1. Each element is composed of extremely small particles called atoms.
2. All atoms of the same element are identical, but the atoms of one element are different from the atoms of all other elements.

3. Atoms of one element cannot be changed into atoms of a different element by chemical reactions.  In addition, atoms are neither created nor destroyed in chemical reactions.
4. Compounds are formed when atoms of more than one element combine.  A given compound will always have the same elements combined in the same exact ratio.

 

 

Modern Atomic Theory

            The current atomic theory states that an atom is composed of three fundamental particles; protons, neutrons, and electrons.  The protons and neutrons combine to form a small but very dense mass in the center of the atom known as the nucleus.  The electrons spin around the nucleus at blindingly fast speeds (close to the speed of light).  Since the electrons are moving so fast, we speak of them as having a probability “cloud” where they are likely to be.

Subatomic Particles:  The Components of an Atom

Particle	Symbol	Charge	Mass (amu)	Location in Atom
Proton	p or p+	+1	1.0073	in the nucleus
Neutron	n or n0	0	1.0087	in the nucleus
Electron	e-	-1	5.486*10-4	orbiting around the nucleus

Isotope:  atoms that have the same number of protons but differing numbers of neutrons and therefore have a different mass.

Isotope Notation	Useful Equations

Energy Levels:  Electrons in atoms occupy different energy levels.  The energy level represents how far away from the nucleus an electron is.  The higher the energy level is, the farther away from the nucleus it is.  (See diagram below)

 

Valence Electrons:  The outermost electrons in an atom.  The number of valence electrons for representative elements is the same as the group number (i.e.-an element in group 5A would have 5 valence electrons).

Trends in the Periodic Table:  The periodic table has trends or patterns for different properties.  The chart below shows some of the more important trends.  The direction of the arrows indicates the direction of increase in that trend.