Section 1-2

Atoms, Bonding, and the Periodic Table

L.1.2.1. Explain how the reactivity

of elements is related to valence electrons in atoms.

L.1.2.2. State what the periodic table tells you about atoms and the properties of elements.

Objectives

Valence Electrons and Bonding

The valence electrons are the ones held at the highest energy level and held the most loosely.

The number of valence

electrons in an atom determine many of the properties of that atom and how it will react with other atoms. Objective L.1.2.1

Valence Electrons

Electron Dot Diagram

An electron dot diagram includes the chemical symbol for the element and is surrounded by dots that represent valence electrons.

Chemical Bonds and Stability

Atoms become stable when their valence electron shells are full. To do this atoms form chemical bonds. A chemical bond is the force of attraction that holds two or more atoms together by the rearrangement of electrons between them.

Chemical Bonds and Chemical Reactions

When atoms bond electrons are either transferred from one to another or shared between them. This is a chemical reaction. This results in the formation of a new substance, usually a compound.

The Periodic Table

Information On Each Element

All Periodic Tables will contain at least the following information about the elements:

Atomic Number Atomic Symbol Name of the Element Atomic Mass

Some Other Elements

What Do These Tell Us?

What are some other informations given on

the periodic table on pages 14 and 15. Atomic mass, number, symbol and name. Whether the element is a metal, nonmetal or

metalloid. Whether it’s a solid liquid or gas at room

temperature. If it’s natural or man made. It’s group and period.

Look On Pages 14 and 15

Each Element is represented by an Atomic

Symbol which is usually represented by 1 or 2 letters.

Each element will also have an Atomic Number which is THE NUMBER OF PROTONS IN THAT ELEMENT!!!!

Each element will also have an Atomic Mass. This number will often be a decimal but we will simply round it to the nearest whole number for now.

Organizing The Elements

The rows across the periodic table are called

periods. As you go across the row from left to right, notice the atomic number increases by one for each element. What does this mean about the number of protons.

They also increase by one, why? Because the atomic number IS THE NUMBER OF

PROTONS! Because the number of electrons is equal to the

number of protons we can say they also increase by one as you move across the row.

Periods And Groups

Elements in the same column are called

a group or family. Each column has a number above it to

identify which group of family it belongs to.

Each group has similar chemical characteristic shared by all of the elements in that group.

Periods And Groups

As the number of protons-the

atomic number-increases, the number of electrons also increases. As a result, the chemical properties of the elements change in a regular way across the periods.

Objective L.1.2.2.

How The Periodic Table Works

Each period ends with the valence

electron shell full. Each period starts with a higher energy

level and one valence electron. Because of this repeating pattern, each

element has a corresponding number of electrons in it’s valence shell.

How The Periodic Table Works

Group 1

Group 1

What did you notice about

all of the valence shells in Group 1 Atoms?

They all have 1 valence electron.

Group 1

Group 2

Group 2

What did you notice about

all of the valence shells in Group 2 Atoms?

They all have 2 valence electrons.

Group 2

Group 17

Group 17

What did you notice about

all of the valence shells in Group 17 Atoms?

They all have 7 valence electrons.

Group 17

Group 18

Group 18

What did you notice about

all of the valence shells in Group 8 Atoms?

They all have 8 valence electrons.

Group 18

The group 18 elements are called

Noble Gases. They are called this because they are highly non-reactive with other elements. That means they tend not to chemically bond with other elements. Why do noble gases tend not to bond with other elements?

Because their valence shells are full.

Noble Gases

Group 17 elements are called Halogens. How

many electrons do they need to fill up their valence shell?

One. These elements would like to gain 1 electron to become stable.

The other end (group 1) of the periodic table elements are called Alkali Metals. How many electrons would they like to lose to become stable?

One. These elements would like to lose an electron.

Reactive Metals and Nonmetals

Sodium and Chlorine

Atoms Are Lazy!

Atoms will always gain or lose electrons dependent on which is easier (requiring less energy).

If a valence shell needs 8 electrons to be stable what will the atom do if it has 2? What is easier, gaining 6 or losing 2?

Losing 2. What if an atom has 7? Should it lose 7 or gain

1? Gain 1.

The elements in the middle part of the

periodic table are the transition metals. How reactive they are depends on how

easily they lose electrons. Some metals like iron, manganese, and

copper are reactive, especially with oxygen while others like gold and platinum are nonreactive.

Other Metals

Nonmetals gain electrons to become

stable. Where do they get the electrons from?

Metals Nonmetals can bond with other

nonmetals but if neither element is willing to give any electrons is there another option for them?

They can share electrons

Other Nonmetals

What Divides The Metals From Nonmetals

Metalloids

Metalloids border the zig zag line separating the metals from nonmetals.

They can have properties of either metals or nonmetals depending on conditions.

Hydrogen

Even though hydrogen is located on the metals side of the periodic table it is definitely a nonmetal.

It’s located over group 1 because it has one valence electron.

1a. What are valence electrons? Valence electrons are the ones with the highest

energy level, are held the most loosely and are responsible for bonding between atoms.

1b. What role do valence electrons play in chemical bonding?

Valence electrons determine how atoms will bond and with what. They can be transferred or shared.

1c. Do oxygen atoms become more or less stable when they form compounds?

Sec. 1-2 Assessment

When oxygen forms compounds it either gains or

shares electrons to fill up the valence shell and become stable.

2a. Using the words period and group, summarize the periodic table.

The rows are called periods and atomic numbers increase by one as you move from left to right. Columns are called groups and elements in a group have the same number of valence electrons which gives them similar chemical properties.

Sec. 1-2 Assessment

2b. Why do the properties of elements change

in a regular way across the periods? (Rows) Because the number of valence electrons

change is a repeating pattern. 2c. How reactive are elements in group 18

(Noble Gases) and how can you explain this in terms of valence electrons?

They are not reactive because their valence shells are already full and therefore stable.

Sec. 1-2 Assessment

How Are We Doing?