Chemistry: 2.1-2.3

Question 1

STONE AGE

Answer 1

First chemists lived in the Middle East before 8000 BC in the Stone Age where humans used only stone tools. But after learning how to start and control fire, they discovered how to change substances: like cooking food. By the end of the Stone Age, metals had been discovered.

Question 2

BRONZE AGE

Answer 2

Chemists in the past only studied matter that had high value to humans, and many of them were metals like gold and copper. Gold was prized for its attractive colour and lustre, while copper was useful for making pots, coins, and tools. Later, experiments with copper led to the development of a strong material known as bronze.

Around 1200 BC, the Hittites, a group of people from the Middle East, discovered how to extract iron from rocks.

Question 3

IRON AGE

Answer 3

People learned to combine iron and carbon to make steel. This created sharper blades for hunting and stronger armor for war.

Question 4

Alchemist­

Answer 4

An ancient scientist who was thought to be part chemist ­ part magician.

Question 5

Atomic Number

Answer 5

Represents the number of protons (positively charged) in the
the nucleus of one atom of the element.
Because an atom is neutral (charges balance), an oxygen atom must also have 8 electrons.
Therefore, the atomic number also represents the number of electrons.

Question 6

Atomic Mass

Answer 6

Represents the total mass of all the protons and neutrons in an atom.
Electrons are so tiny that they have very little effect on the total mass of the atom.

Question 7

Mass Number

Answer 7

Represents the sum of all the protons and neutrons in an atom.
More often than not, Atomic Mass = Mass Number
Mass Number ­- Atomic Number = Number of Neutrons.

Question 8

Group (or Family)

Answer 8

Columns numbered 1 to 18. The elements belonging to the same
group have similar properties (Sodium and Potassium have similar properties). Groups
are named by the first element in the column. For example, Group 10 is the Nickel Group.

Question 9

Hydrogen

Answer 9

Hydrogen is an exception. Even though it is in Group 1, it is very different from the other elements in Group 1. For this reason, many periodic tables place hydrogen in a separate spot away from the other elements.

Question 10

Period

Answer 10

Rows numbered 1 to 7. Within the periods, there is a pattern. As you move
across the periodic table, the properties of the elements change. They gradually
change from metals to non­metals. The most reactive metals start on the left. As
you move to the right, the metals become less reactive.

Question 11

Metals

Answer 11

These elements are shiny, hammered, and deformed. They conduct electricity and are good thermal conductors.

Question 12

Alkalis - Group 1

Answer 12

These metals are the most reactive of the metals. They react when exposed to air or water. As you move down the group from lithium ­ the reactivity increases.

Question 13

Transition Metals - Groups 3 to 12

Answer 13

These metals have a strong tendency to form compounds and many of their compounds are coloured.

Question 13

Alkaline­-Earth (Group 2)

Answer 13

These metals react when exposed to air and water too; but their reactivity is not as strong.

Question 14

Non-­Metals

Answer 14

These elements can be a solid or a gas. The solid ones are dull and brittle. Non­Metals do not conduct electricity and are good insulators.

Question 15

Halogens (Group 17)

Answer 15

These non­metals are the most reactive, however, they can undergo a chemical change to form useful properties. For example, fluorine will react with sodium to form sodium fluoride (the chemical in toothpaste).

Question 16

Noble Gases or Inert Gases (Group 18)

Answer 16

These non­metals are the most stable and
unreactive elements. Scientists used to believe that noble gases could never combine with other
elements. However, in 1962, a chemist named Neil Bartlett made the first noble gas compound.

Question 17

Metalloids

Answer 17

These elements have bothmetallic and non­metallic properties.

Question 18

Ion

Answer 18

An atom with an electric charge. It is NOT neutral.

Question 19

Ion Charge

Answer 19

The electrical charge of an ion is created by the gain (negative charge) or loss (positive charge) of one or more electrons from an atom.
An oxygen atom has an ion charge of ­2.

This means it has gained 2 electrons.

Question 20

Step 1: Looking for a Pattern

Answer 20

In the 1700s, early chemists used symbols of the Sun and planets to represent the
seven metallic elements known at the time.

By the early 1800s, more than 30elements had been identified. Chemists tried to
group the elements according to their properties.

John Dalton developed this new set of symbols for elements,
which improved communication between chemists around the
world.

Berzelius modified Dalton’s work. He suggested using lettersrather than
pictures to represent each element.

• The first letter (upper case) of an element would become the symbol.
• For elements with the same first letter, such as hydrogen and helium, a
  second letter (lower case) would be added.

John Dalton

Jons Jacob Berzelius

Berzelius naming system is the one we use today.
His system enabled chemists to communicate with
each other in an understandable manner.