Atomic Structure & the Periodic Table

Basic Definitions

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

• Atoms are made up of several subatomic particles called protons, neutrons, and electrons

Protons, Neutrons, & Electrons

• Protons – have a +1 charge and are found in the nucleus of the atom

• Neutrons – have no charge and are also found in the nucleus of an atom

• Electrons – have a -1 charge and are found on the outside of the nucleus

• Nucleus – made up of protons and neutrons, has an overall + charge

Atomic Structure

Atomic Numbers

• The atomic number of an element is the number of protons in the nucleus of an atom of that element.

• It is the number of protons that determines the identity of an element, as well as many of its chemical and physical properties.

• The number of protons for an element CANNOT be changed.

Atomic Numbers

• Because atoms have no overall electrical charge, the number of protons must equal the number of electrons.

• Therefore, 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 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 – 1

– Which 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 columns– Groups – vertical columns– Periods – horizontal rows

Group Names

Group Name

1A2A6A7A8A

Alkali MetalsAlkaline Earth MetalsChalcogensHalogensNoble Gases

Groups

• The group tell you the number of valence electrons that the element has

• Valence electrons are 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.

• With the exception of tin, lead, and bismuth, metals have one, two, or three valence electrons. Metal Video Clip

Metals

• 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 (coded blue) 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 Various oxidation

States Video Clip

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

Non Metals

• Although the majority of the elements in the periodic table are metals, many nonmetals are abundant in nature

• The nonmetals oxygen and nitrogen make up 99 percent of Earth’s atmosphere.

• 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.