Chapter 1

Chemistry: Matter and Measurement

ByDr AYESHA MOHY-UD-DIN

IN THE NAME OF ALLAH, THE BENEFICENT THE MERCIFUL

Approaching Chemistry,

Elements and the Periodic Table

Elements and the Periodic Table

• Classification is arranging items into groups or categories according to some criteria.

• The act of classifying creates a pattern that helps you recognize and understand the behavior of fish, chemicals, or any matter in your surroundings.

• Matter is usually defined as anything that has mass and occupies space.

• Chemistry is the study of the composition, properties and transformation of matter.

• Scientific Approach consists of Hypothesis, Experiment, Inference, Prediction (Theory/Law)

– An Intensive property is one which do not depend on amount of substance

– An Extensive property is one which depend on amount of substance

– A physical change is a change that does not alter the identity of the matter.

– A chemical change is a change that does alter the identity of the matter.

– An element is a pure substance which cannot be broken down into anything simpler by either physical or chemical means.

– A compound is a pure substance that can be decomposed by a chemical change into simpler substances with a fixed mass ratio

• Sugar (A) is a compound that can be easily decomposed to simpler substances by heating. (B) One of the simpler substances is the black element carbon, which cannot be further decomposed by chemical or physical means.

• Elements

• Names of Elements– The first 114 elements have internationally accepted

names, which are derived from:• The compound or substance in which the element was

discovered

• An unusual or identifying property of the element

• Places, cities, and countries

• Famous scientists

• Greek mythology

• Astronomical objects.

• The elements Oxygen and Silicon make up about 75% of the earth's solid surface. Water on the surface and in the air as clouds and fog is made up of hydrogen and oxygen. The air is 99% nitrogen and oxygen. Hydrogen, oxygen, and carbon make up 90% of a person. Thus almost everything you see in this picture us made up of just six elements.

– Chemical Symbols• There are about a dozen common elements that have

single capitalized letter for their symbol• The rest, that have permanent names have two letters.

– the first is capitalized and the second is lower case.• Some elements have symbols from their Latin names.• Ten of the elements have symbols from their Latin or

German names.

• Here are some of the symbols Dalton used for atoms of elements and molecules of compounds. He probably used a circle for each because, like the ancient Greeks, he thought of atoms as tiny, round hard spheres.

SymbolAtomic Mass

Atomic Number

HHydrogenHydrogen

1

1

CdCadiumCadium

112

48

AntimonyAntimony

Sb122

51

AntimonyAntimony

Am243

95

• The Periodic Law

The History of the Modern

Periodic Table

During the nineteenth century, chemists began to categorize

the elements according to similarities in their physical and chemical properties. The end result of these studies was our

modern periodic table.

Johann Dobereiner

1780 - 1849

Model of triads

In 1829, he classified some elements into groups of three, which he called triads.The elements in a triad had similar chemical properties and orderly physical properties.

(ex. Cl, Br, I andCa, Sr, Ba)

John Newlands

1838 - 1898

Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

Dmitri Mendeleev

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

Lothar Meyer

1830 - 1895

At the same time, he published his own table of the elements organized by increasing atomic mass.

• Dmitri Medeleev gave us a functional scheme with which to classify elements.– Mendeleev’s scheme was based on chemical properties

of the elements.– It was noticed that the chemical properties of elements

increased in a periodic manner.– The periodicity of the elements was demonstrated by

Medeleev when he used the table to predict to occurrence and chemical properties of elements which had not yet been discovered.

• Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.

• The Periodic Law– Similar physical and chemical properties recur

periodically when the elements are listed in order of increasing atomic number.

• The Modern Periodic Table

Henry Moseley

1887 - 1915

In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.*“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

• Introduction– The periodic table is made up of rows of elements and

columns.– An element is identified by its chemical symbol.– The number above the symbol is the atomic number– The number below the symbol is the rounded atomic

weight of the element.– A row is called a period– A column is called a group

• (A) Periods of the periodic table, and (B) groups of the periodic table.

– Each period ends with a completely filled outer shell that has the maximum number of electrons for that shell.

– The number identifying the A families identifies the number of electrons in the outer shell, except helium

– The outer shell electrons are responsible for chemical reactions.

– Group A elements are called representative elements– Group B elements are called transition elements.

• Chemical “Families”– IA are called alkali metals because the react with water

to from an alkaline solution– Group IIA are called the alkali earth metals because

they are reactive, but not as reactive as Group IA.• They are also soft metals like Earth.

– Group VIIA are the halogens• These need only one electron to fill their outer shell

• They are very reactive.

– Group VIIIA are the noble gases as they have completely filled outer shells

• They are almost non reactive.

• Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).

Metal: Elements that are usually solids at room temperature. Most elements are metals.Non-Metal: Elements in the upper right corner of the periodic Table. Their chemical and physical properties are differentfrom metals.

Metalloid: Elements that lie on a diagonal line between the Metals and non-metals. Their chemical and physical properties are intermediate between the two.

The periodic table is the most important tool in the chemist’s

toolbox!

• PROBLEM 1.1 • Look at the alphabetical list of elements inside

the front cover, and find the symbols for the following elements:

• (a) Cadmium (used in batteries)• (b) Antimony (used in alloys with other metals)• (c) Americium (used in smoke detectors)

• PROBLEM 1.2 • Look at the alphabetical list of elements inside

the front cover, and tell what elements the following symbols represent:

• (a) Ag (b) Rh (c) Re (d) Cs (e) Ar (f) As

• PROBLEM 1.3

• Identify the following elements as metals, nonmetals, or semimetals:

• (a) Ti (b) Te (c) Se (d) Sc (e) At (f) Ar

• 1.28 How many elements are presently known? About how many occur naturally?

• 1.29 What are the rows called and what are the columns called in the periodic table?

• 1.30 How many groups are there in the periodic table? How are they labeled?

• 1.31 What common characteristics do elements within a group of the periodic table have?

• 1.32 Where in the periodic table are the main-group elements found? Where are the transition metal groups found?

• 1.33 Where in the periodic table are the metallic elements found? Where are the nonmetallic elements found?

• 1.34 What is a semimetal, and where in the periodic table are semimetals found?

• 1.35 List several general properties of the following:• (a) Alkali metals• (b) Noble gases• (c) Halogens• 1.36 Without looking at a periodic table, list as many

alkali metals as you can. (There are five common ones.)

• 1.37 Without looking at a periodic table, list as many alkaline earth metals as you can. (There are five common ones.)

• 1.38 Without looking at a periodic table, list as many halogens as you can. (There are four common ones.)

• 1.39 Without looking at a periodic table, list as many noble gases as you can. (There are six common ones.)

• 1.40 What are the symbols for the following elements?

• (a) Gadolinium (used in color TV screens)• (b) Germanium (used in semiconductors)• (c) Technetium (used in biomedical imaging)• (d) Arsenic (used in pesticides)• 1.41 What are the symbols for the following

elements?• (a) Cadmium (used in rechargeable batteries)• (b) Iridium (used for hardening alloys)• (c) Beryllium (used in the space shuttle)• (d) Tungsten (used in lightbulbs)

• 1.42 Give the names corresponding to the following symbols:

• (a) Te (b) Re (c) Be (d) Ar (e) Pu• 1.43 Give the names corresponding to the following

symbols:• (a) B (b) Rh (c) Cf (d) Os (e) Ga• 1.44 What is wrong with each of the following

statements?• (a) The symbol for tin is Ti.• (b) The symbol for manganese is Mg.• (c) The symbol for potassium is Po.• (d) The symbol for helium is HE.

• 1.45 What is wrong with each of the following statements?

• (a) The symbol for carbon is ca.• (b) The symbol for sodium is So.• (c) The symbol for nitrogen is Ni.• (d) The symbol for chlorine is Cr.