Chem 109 - General Chemistry - Spring 2015
Lecture Notes 6: 2 February
Chemical Nomenclature, cont.
First, let's look at the the elements that you should learn the names of, as listed on the web:
The common ions and acids and bases are summarized on the handout and the web:
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.
Periodic Table and common ion charges:
- For positive atomic ions the charge is often the Group number,
- Group 1 always = +1 (e.g. Na+1 )
- Group 2 always = +2 (e.g. Ca+2 )
- For negative atomic ions the charge is often the group number –18,
- Group 17 = 17–18= –1 (e.g. Cl–1 )
- Group 16 = 16–18 = –2 (e.g. S–2 )
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 Ionsfor 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
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:
||9.11 x 10-28g
|Proton (p or H+)
||1.67 x 10-24g
|| 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 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:
You should be able to fill in the blanks in a table like this, with the aid of a periodic table, on a quiz.
Look at the Periodic Chart.
- 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, BH3, CH4, H3N, H2O, HF.
- Group IA always +1
- Group IIA always +2
- Group IIIA commonly +3, Al always+3
- Group IV +4 or -4 (usually covalent)
- Group VA commonly -3
- Group VIA commonly -2
- Group VIIA commonly -1
- Metal oxides are basic combined with water (e.g. NaOH, KOH), non-metal oxides are 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.
Periodic Table of the Elements
© R A Paselk
Last modified 2 February 2015