Atomic Structure & the Periodic Table

Democritus (460-370 BC)

The first to propose that matter was not infinitely indivisible

Believed that matter was made up of atomos (or atoms)

He also said that atoms could not be created or destroyed

Democritus’ Theory

1. Matter is composed of empty space through which atoms move

2. Atoms are solid, homogeneous, indestructible, and indivisible

3. Different atoms have different sizes and shapes4. The differing properties of matter are due to the

size, shape, and movement of atoms5. Changes in matter result from changes in the

groupings of atoms and not the atoms themselves

John Dalton

John Dalton was the next scientist to propose a theory about the atom in the 19th century

Dalton’s Atomic Theory

1. All matter is composed of extremely small particles called atoms

2. All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of a specific element are different from other elements

3. Atoms cannot be created, destroyed, or broken into smaller particles

4. Different atoms combine in simple whole number ratios to form compounds

5. In a chemical reaction, atoms are separated, combined, or rearranged

History of Atomic Structure

Scientist Experiment Knowledge Obtained

Crookes Cathode Ray Tube

Neg. particles of some kind exist

J.J. Thomson Cathode Ray Deflection

Mass/Charge ratio of electron

Millikan Oil Drop Experiment

Charge of electron

Rutherford Gold Foil Experiment

Nucleus present

Basic Definitions

Atom – smallest unit of an element that retains the properties of that element

Atoms - made up of several subatomic particles: protons, neutrons, and electrons

Protons, Neutrons, & Electrons

Protons +1 charge found in the nucleus of the atom

Neutrons no charge found in the nucleus of an atom

Electrons -1 charge found on the outside of the nucleus

Nucleus made up of protons and neutrons overall + charge

Atomic Structure

Atomic Numbers

Atomic number (Z) - number of protons in the nucleus of an atom of that element.

The number of protons determines the identity of an element

The number of protons for an element CANNOT be changed.

Atomic Numbers

Atoms have no overall electrical charge so the number of protons must equal the number of electrons.

So, the atomic number of an element also tells the number of electrons in a neutral atom of that element.

The number of electrons can be changed when determining the charge of an ion.

Masses

The mass of a neutron is almost the same as the mass of a proton.

The sum of the protons and neutrons in the nucleus is the mass number (A) of that particular atom.

Isotopes of an element have different mass numbers because they have different numbers of neutrons, but they all have the same atomic number (number of protons & electrons)

Isotopes

When writing isotopes, the atomic number (or number of protons) will appear at the bottom left of the formula

The mass number (number of protons plus neutrons will appear at the top left of the formula.

The element symbol will appear to the right of the numbers

The different number of neutrons has NO bearing on chemical reactivity

Writing the Names of Isotopes

When writing the name of an isotope, you will write the name of the element – the mass number

For example 126 C would be named:

Carbon - 12

6

12

6

12C612

Try the following

Name Symbol # Protons # Neutrons # Electrons Mass #

Carbon – 11

197

Au

79

1 2

25 55

Oxygen - 15

Try the following

Name Symbol # Protons # Neutrons # Electrons Mass #

Carbon – 11 11

C

6

6 5 6 11

Gold - 197 197

Au

79

79 118 79 197

Hydrogen – 3

3

H

1

1 2 1 3

Manganese - 55

55

Mn

25

25 30 25 55

Oxygen - 15 15

O

8

8 7 8 15

Try this one

Name Symbol # Protons # Neutrons # Electrons Mass #

Iodine -1 - 130

Try this one

Name Symbol # Protons # Neutrons # Electrons Mass #

Iodine -1 - 130 130

I -1

53

53 77 54 130

Atomic Mass

Atomic mass –the weighted average mass of all the naturally occurring isotopes of that element.

The number is usually located at the bottom of the periodic table and has decimal places

Calculating Atomic Mass

Calculating Atomic Mass

Copper exists as a mixture of two isotopes.

The lighter isotope (Cu-63), with 29 protons and 34 neutrons, makes up 69.17% of copper atoms.

The heavier isotope (Cu-65), with 29 protons and 36 neutrons, constitutes the remaining 30.83% of copper atoms.

Calculating Atomic Mass

First, calculate the contribution of each isotope to the average atomic mass, being sure to convert each percent to a fractional abundance.

The average atomic mass of the element is the sum of the mass contributions of each isotope.

Calculating Atomic Mass

Try this one…

Calculate the atomic mass of germanium.

72.59 amu

You can tell many things from an isotope formula

Hydrogen has three naturally occurring isotopes in nature: Hydrogen – 1, Hydrogen – 2, and Hydrogen – 3.Which is the most abundant in nature?

Hydrogen – 1Which is the heaviest?

Hydrogen - 3

Periodic Table

Periodic Table – arrangement of elements in order of increasing atomic number with elements having similar properties in vertical columnsGroups – vertical columnsPeriods – horizontal rows

Group Names

Group Name

1A2A6A7A8A

Alkali MetalsAlkaline Earth MetalsChalcogensHalogensNoble Gases

Groups

The group tells you the number of valence electrons that the element has

Valence electrons - electrons in the outermost shell of the atom

All group 1A elements have 1 valence electron. Likewise, all group 8A elements have 8 valence electrons.

Characteristics

Elements in the same group exhibit similar chemical characteristics due to the fact that they all have the same number of valence electrons.

The most stable number of valence electrons is 8

This is called an octet

Charges

Every element wants 8 valence electrons to become stable. They will gain or lose valence electrons to form an octet

For example…Group 1A elements have 1 valence electron. They can either gain 7 electrons to have an octet or lose 1.

What is easier?Lose 1

If an element loses 1 electron (1 negative charge) what charge will the resulting ion have?+1

Charges

Let’s go to group 7A. This group has 7 valence electrons

It can either loose 7 or gain 1 What is the easiest?

Gain 1

What will be the resulting charge if the element gain 1 electron (1 negative charge)?-1

Physical States and Classes of the Elements

The majority of the elements are metals. They occupy the entire left side and center of the periodic table.

Nonmetals occupy the upper-right-hand corner.

Metalloids are located along the boundary between metals and nonmetals.

Metals

Metals are elements that have luster, conduct heat and electricity, and usually bend without breaking.

All metals except mercury are solids at room temperature; in fact, most have extremely high melting points.

The periodic table shows that most of the metals are not main group elements.

Transition Metals

The elements in Groups 3 through 12 of the periodic table are called the transition elements.

All transition elements are metals.

Many transition metals can have more than one charge

Inner Transition Metals

In the periodic table, two series of elements, atomic numbers 58-71 and 90-103, are placed below the main body of the table.

These elements are separated from the main table because putting them in their proper position would make the table very wide.

The elements in these two series are known as the inner transition elements.

The first series of inner transition elements is called the lanthanides because they follow element number 57, lanthanum.

The second series of inner transition elements, the actinides, have atomic numbers ranging from 90 (thorium, Th) to 103 (lawrencium, Lr).

Inner Transition Metals

Most nonmetals don’t conduct electricity, are much poorer conductors of heat than metals, and are brittle when solid.

Many are gases at room temperature; those that are solids lack the luster of metals.

Their melting points tend to be lower than those of metals.

Non Metals

Properties of Metals and Nonmetals

Metalloids

Metalloids have some chemical and physical properties of metals and other properties of nonmetals.

In the periodic table, the metalloids lie along the border between metals and nonmetals.