Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2011

Lecture Notes 5: 28 January

Chemical Periodicity

Look at the Periodic Chart.

Periods

The rows are referred to as periods. The pattern arises due to a repetition or periodicity of chemical properties.
- Combining ratios with hydrogen. 1 - 4 - 1: LiH, BeH₂, B₃, C₄, H₃N, H₂O, HF.
- Ions:
  1. Group IA always +1
  2. Group IIA always +2
  3. Group IIIA commonly +3, Al always+3
  4. Group IV +4 or -4 (usually covalent)
  5. Group VA commonly -3
  6. Group VIA commonly -2
  7. Group VIIA commonly -1
- Metal oxides basic combined with water (e.g. NaOH, KOH), non-metal oxides acidic combined with water (e.g. SO₂ and water gives H₂SO₃, one of the important acids in acid rain).
  - IA & IIA oxides are basic, combining with water to give compounds such as NaOH and Mg(OH)₂, while VIA & VIIA oxides form acids with water such as H₂SO₄ and HClO₄. Intermediate groups show transitional behavior, e.g. carbon froms a weak acid, nitrogen strong acid, aluminum a weak base, phosphorous a weak acid, sulfur a strong acid.
- Properties go from metallic in Group IA to non-metallic in VIIIA.

Groups

The vertical columns of elements on the table sharing a family resemblance of properties (e.g. Li - Fr) are called groups. For example:
- IA (1) = alkali metals;
- IIA (2) = Alkaline earth metals;
- VIIA (17) = Halogens (note the generic symbol of X standing for any halogen);
- Group VIII (18) is known as the Noble Gases, or sometimes the Inert Gases because until the 1960's they had no known compounds. Very unreactive and only known compounds are with very reactive elements like F and O, and even they don't form compounds with smaller Noble gases such as He and Ne.
Note the numbering of the groups. The numbers from 1 - 18 are the internationally accepted numbers. We will also use the I - VIII "American" numbering system for the representative elements.

Terms etc.:

Representative elements: the elements of the s-block and p-block ("tallest" columns, blue and green on the table below).
Transition metal elements: the elements of the d-block (yellow in the table below).
Inner-transition metal elements: The Lanthanides and Actinides (not shown on the table below)

Periodic Table of the Elements

IA IIA IIIA IVA VA VIA VIIA VIIIA

H He

Li Be B C N O F Ne

Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB Al Si P S Cl Ar

K Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Ag Cd Sn I Xe

Cs Ba W Pt Au Hg Pb

**Periodic Table of the Elements**
IA	IIA		IIIA	IVA	VA	VIA	VIIA	VIIIA
H	He
Li	Be		B	C	N	O	F	Ne
Na	Mg	IIIB	IVB	VB	VI	VIIB	VIIIB	IB	IIB	Al	Si	P	S	Cl	Ar
K	Ca		Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr									Ag	Cd		Sn			I	Xe
Cs	Ba				W				Pt	Au	Hg		Pb

Chemical Nomenclature

Nomenclature is covered in section 2.8 (pp 57-67) in your textbook-you should be able to do the examples and exercises in the assigned problems. Note also the Discussion Module, OWL and these notes.

First, let's look at the the elements that you should learn the names of, as listed on the web:

HSU Chemistry Elements Names

The common ions and acids and bases are summarized on the handout and the web:

HSU Chemistry Table of Ions & HSU Chemistry Table of Acids

Note that formulae are more or less written with the elements ordered by electronegativity (elements on the right side precede those on the left).

Covalent vs. Ionic compounds:

In covalent compounds atoms have a definite relationship to each other, they are "married." Thus for water, H₂O, the smallest particle is a water molecule containing one oxygen atom and two hydrogen atoms.
In ionic compounds ions of opposite charge attract each other, but there is no definite attachment, just a constant ratio. Thus in sodium chloride crystals each sodium ion is surrounded by six chloride ions and each chloride ion is surrounded by six sodium ions and they are equally attracted by each - there is no one-to-one relationship.

This distinction will be important in some aspects of naming chemical compounds.

IUPAC vs traditional names

There are two common naming systems:

The IUPAC/Stock system

This is the modern, systematic scheme developed by the International Union of Pure and Applied Chemists.

In this system the positively charged elements in a compound are named as the element name followed by the "apparent charge" (later we will see this really refers to something called the oxidation number which often = charge) written in Roman numerals enclosed in brackets. Thus iron two-plus = iron (II) and iron three-plus = iron (III). Elements which exhibit only one charge do not require that the charge be shown. Thus sodium one-plus = Na, magnesium two-plus = Mg and aluminum three-plus = Al. (Recall that the alkali metals are always plus one or zero and the alkaline earth metals are always plus two or zero.) Look at the HSU Chemistry Table of Ions for additional ions.
For negatively charged single atom ions the ending -ide is placed on the beginning of the element name. Thus chlorine one-minus becomes chloride, and similarly we see fluoride, bromide and iodide, while the two-minus charge ions of Group VIA become oxide, sulfide, etc.

Recognize these traditional names for metal ions:

Fe(II) = ferrous
Fe(III) = ferric
Cu(I) = cuprous
Cu(II) = cupric
Hg(I) = mercurous (Hg₂²⁺)
Hg(II) = mercuric
Sn(II) = stannous
Sn(IV) = stannic
Pb(II) = plumbous
Pb((IV) = plumbic

FYI - Nomenclature examples etc.

Polyatomic ions

In these ions a group of atoms are covalently bound to each other and functions as a single charged particle. You should memorize the following names and be able to write formulas for the compounds and vice versa:

ammonium ion:
cyanide ion:
carbonate ion:
nitrate ion:
nitrite ion:
phosphate ion:
sulfite ion:
oxalate ion:
hydroxide ion:
acetate ion:
bicarbonate ion:
sulfate ion:

Compounds

Salts (Ionic Compounds) and Bases

Ions of opposite charge may combine to form neutral compounds. Thus the ions must combine in ratios such that the charges cancel. When the negative ion is hydroxide, the compound is considered a base. Examples:

potassium chloride:
sodium hydrogen sulfate (sodium bisulfate):
aluminum hydroxide:
iron(III) carbonate:
iron(III) hydrogen carbonate (iron(III) bicarbonate):
ammonium phosphate:
copper(I) oxalate:
calcium hydroxide:

Acids

Acids are compounds which give hydrogen ions (protons) in solution. There are two common inorganic acid types in terms of nomenclature:

Hydro-( )-ic acids: If hydrogen combines with a nonmetallic element the resulting acid is named by adding the prefix hydro- and replacing -ide by -ic. Examples:
- HBr:
- HCl:
Oxo acids: When non-metallic elements react with oxygen the resulting products often react with water or form ions which can react with protons to from acids. These oxo acids are named by replacing the -ate suffix with -ic acid or -ite suffix with -ous acid. Examples:
- carbonic acid:
- sulfuric acid:
- acetic acid:
- nitric:
- Chloroacids (Hydrochlorous acid - Perchloric acid)

The HSU Chemistry Table of Common Acids is a useful summary of the acids you should be familiar with.

Special names

These compounds don't follow the rules, but have been in common use so long they keep their traditional names. Examples:

Water:
methane:
ammonia:
hydrogen peroxide:

The Nuclear Atom

Atoms are now known to consist of three different types of particles: electrons, protons and neutrons (the common form of one very important atom, hydrogen, has only two kinds: a proton and an electron). The protons and neutrons reside in a small inner portion called the nucleus while the electrons reside in a relatively large cloud centered on the nucleus. Important properties of these particles are listed in the table below:

Particle	Charge	Relative Mass	Mass
Electron (e^-)	-1	1/1840	9.11 x 10^-28g
Proton (p or H⁺)	+1	ª1	1.67 x 10^-24g
Neutron (n)	0	ª1	1.67 x 10^-24g

Some important terms which you must know are:

Atomic number (Z) - the number of protons in the nucleus. This number is characteristic of a given element.
Atomic mass number (A) - the sum of the protons and neutrons in a given atom (p + n).
Atomic mass - the actual mass of an average atom in a sample. The characteristic atomic masses for Earth are shown on periodic tables.
Atomic Mass Unit: the atomic mass unit = amu is a unit of mass for atoms. It is defined as 1/12 the mass of one atom of ¹²C, where the mass of ¹²C is defined as 12 exactly.

Isotopes

Isotopes are forms of elements which differ only in the number of neutrons. This means different isotopes of the same element have essentially the same chemical properties but slightly different physical properties. They can also differ substantially in terms of their nuclear stability. Let's look at some examples of isotopes:

Symbol Z A p n e^-

¹⁴C 6 14 6 8 6

²³⁸U⁶⁺ 92 238 92 146 86

³⁵Cl^- 17 35 17 18 18

¹⁸O^2- 8 18 8 10 10

You should be able to fill in the blanks in a table like this with, the aid of a periodic table, on a quiz.

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© R A Paselk

Last modified 28 January 2011