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.

• Classifying Matter

• Matter is usually defined as anything that has mass

and occupies space.

Gas Liquid Solid

Total disorder

Lots of empty space

Disorder

Some space

Particles closer

together

Order

Particles fixed

in position

• Solids, Liquids, and Gases

– Gases have no defined shape or defined volume

• Low density

– Liquids flow and can be poured from one container to

another

• Indefinite shape and takes on the shape of the container.

– Solids have a definite volume

• Have a definite shape.

• Mixtures and Pure Substances

– A mixture has unlike parts and a composition that varies

from sample to sample

– A heterogeneous mixture has physically distinct parts

with different properties.

– A homogeneous mixture is the same throughout the

sample

– Pure substances are substances with a fixed composition

• A classification scheme for matter.

– 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.

– A compound is a pure substance that can be decomposed

by a chemical change into simpler substances with a

fixed mass ratio

– An element is a pure substance which cannot be broken

down into anything simpler by either physical or

chemical means.

• 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.

Isopropyl alcohol is a

A. heterogeneous mixture

B. homogeneous mixture

C. pure substance

D. Compound

E. pure substance and compound

EXAMPLE

E

• Elements

• Reconsidering the Fire Element

– The phlogiston theory viewed phlogiston as a

component of all matter.

– The burning of a material was considered to be the

escaping of phlogiston from the matter.

– If a material did not burn, it was considered to contain no

phlogiston.

• The phlogiston theory.

(A) In this theory,

burning was considered

to be the escape of

phlogiston into the air.

(B) Smelting combined

phlogiston-poor ore with

phlogiston from a fire to

make a metal. (C) Metal

rusting was considered to

be the slow escape of

phlogiston from a metal

into the air.

• Discovery of Modern Elements

– Antoine Lavoisier suggested that burning was actually a

chemical combination with oxygen.

– Lavoisier realized that there needed to be a new concept

of elements, compounds, and chemical change.

– We now know that there are 89 naturally-occurring

elements and at least 23 short-lived and artificially

prepared.

• Priestley produced a gas (oxygen) by using sunlight to heat

mercuric oxide kept in a closed container. The oxygen

forced some of the mercury out of the jar as it was

produced, increasing the volume about five times.

• Lavoisier heated a measured amount of mercury to form the red oxide of mercury. He measured the amount of oxygen removed from the jar and the amount of red oxide formed. When the reaction was reversed, he found the original amounts of mercury and oxygen.

• Names of Elements

– The first 103 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.

• 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.

• The elements of aluminum, Iron, Oxygen, and Silicon make up about 88 percent 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 percent nitrogen and oxygen. Hydrogen, oxygen, and carbon make up 97 percent of a person. Thus almost everything you see in this picture us made up of just six elements.

Atomic theory

Dalton’s Postulates

1. Every element is composed of tiny particles called atoms

2. All atoms of a given element are identical

1. Atoms of different elements have different properties

3. Atoms of an element are NOT changed into atoms of

another element by chemical processes

1. Matter can neither be created nor destroyed

4. Compounds are formed when atoms of more than one

element combine

Dalton’s Laws

1. The Law of Constant Composition:

“Any given compound always consists of the same

atoms and the same ratio of atoms. For example, water

always consists of oxygen and hydrogen atoms, and

it is always 89 percent oxygen by mass and 11 percent

hydrogen by mass”

2. The Law of Conservation of Mass: “The total mass of materials before and after a chemical

reaction must be the same. For example, if we combine

89 grams of oxygen with 11 grams of hydrogen under

the appropriate conditions, 100 grams of water will be

produced—no more and no less.”

Dalton’s Laws

3. The Law of Multiple Proportions: “If two elements combine to form more than one compound,

the masses of one of the elements that can combine with a given

mass of the other element are related by factors of small whole

numbers”

For example, water has an oxygen-to-hydrogen mass ratio of 7.9:1.

Hydrogen peroxide, another compound consisting of oxygen and

hydrogen, has an oxygen-to-hydrogen mass ratio of 15.8:1.

The ratio of these two ratios gives a small whole number.

MODERN ATOMIC THEORY

– Chemical Symbols

• There are about a dozen common elements that have s

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.

– Symbols and Atomic Structure

• A molecule is a particle that is composed of two or

more atoms held together by a chemical bond.

• Isotopes are atoms of an element with identical

chemical properties, but different masses due to a

difference in the number of neutrons.

• The atomic mass of an element is the average of all

the atomic masses of the isotopes.

– an isotopes contribution is determined by its

relative abundance.

• The mass of an element is the mass of the element

compared to an isotope of carbon Carbon 12.

– Carbon 12 is assigned an atomic mass of 12.00 g.

– 12.00 is one atomic mass unit

• The number of protons and neutrons in an atom is its

mass number.

• Atomic numbers are whole numbers

• Mass numbers are whole numbers

• The atomic mass is not a whole number.

Symbol Atomic Mass

Atomic Number

Charge

(if ion)

H

Hydrogen

1

1

Protons: 1

Neutrons: 0

Electrons: 1

Na

Sodium

23

11

Protons: 11

Neutrons: 12

Electrons: 11

Rhenium

Re 186

75

Protons: 75

Neutrons: 111

Electrons: 75

Rhenium isotope

Re 187

75

Protons: 75

Neutrons: 112

Electrons: 75

EXAMPLE

How many protons, neutrons and electrons are found in an

atom of

133 55 Cs

Atomic number = protons and electrons

There are 55 protons and 55 electrons

Mass number = sum of protons and neutrons

133 – 55 = 78

There are 78 neutrons

• The Periodic Law

• 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

• 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.

• Periodic Patterns

– The chemical behavior of elements is determined by its

electron configuration

– Energy levels are quantized so roughly correspond to

layers of electrons around the nucleus.

– A shell is all the electrons with the same value of n.

• n is a row in the periodic table.

– Each period begins with a new outer electron shell

– 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 different

from 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.

– When an atom or molecule gain or loses an electron it

becomes an ion.

• A cation has lost an electron and therefore has a

positive charge

• An anion has gained an electron and therefore has a

negative charge.

– Elements with 1, 2, or 3 electrons in their outer shell tend

to lose electrons to fill their outer shell and become

cations.

• These are the metals which always tend to lose electrons.

– Elements with 5 to 7 electrons in their outer shell tend to

gain electrons to fill their outer shell and become anions.

• These are the nonmetals which always tend to gain electrons.

– Semiconductors (metalloids) occur at the dividing line

between metals and nonmetals.

What would the charge be on a sodium ion?

EXAMPLE

Since sodium in in Group IA it is a metal and so would

LOSE an electron

You can tell how many would be lost by the group number

Group 1A elements lose 1 electron

So the charge would be +1

Remember an electron is negatively charged. When you lose

them atom becomes positively charged…

when you gain them it becomes negatively charged

How would you right the symbol for the sodium CATION?

EXAMPLE

Na +1

How many outer electrons does sodium have before it

loses one?

It has 1…remember the group number!