Elements ,compounds, and mixtures

Juwarto, S.PdGrade VII Semester 1

115 Junior high Schools

Matter

Pure substance

Element

Compound

Mixture

Homogeneous

Heterogeneous

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Basic Competency:To understand the element, compound and mixture.

Standard Competency:Describes concept of element, compound and mixture.

Objectives:• To describe the characteristics of

elements, compounds, and mixtures• To classify matters into

elements ,compounds ,and mixture

Matter• Matter - anything that has mass and take any space

Examples of element:

Element• Element is single matter that cannot be broken

down into simpler matter by chemical methods.

• There are 116 known elements. Of these 92 are found in the Earth (natural). The other 24 elements have been made by scientist in laboratories (manmade).

Fluorine

Aluminium

Gold

silver

Mercury

The Symbol of element• Jons Jacob Berzelius proposed alphabets as the symbols of

each element. • All of elements use symbol. These symbols were taken one or

two letters from their old Latin or Greek name.

Example: Au is the Latin word of gold “Aurum”.

• Rules of writing element symbols:

1. If an element is symbolized by one letter, it must be capital letter, for example oxygen (O), hydrogen (H), carbon (C).

2. If an element is symbolized by more than one letters, the first letter must be capital letter followed by small letter, for example zinc (Zn), gold (Au), copper (Cu).

Think Time

• What are the chemical symbols of the following elements?a) Bromine f) Mercuryb) Silver g) Calciumc) Uranium h) Natriumd) Antimony i) Potassiume) Tungsten j) Helium

• What are the names of the elements with the following chemical symbols?a) Si f) Nib) P g) Alc) Sn h)Mg d) Pb i) Zne) Au f) S

Classification of the Elements

– Elements can be classified by their physical state at room temperature• Solid (of the 92 natural element, 79 are

solids)• Gas (of the 92 natural element, 11 are

gases)• Liquid (of the 92 natural element, 2 are

liquid)

Chlorine gaseous element

Bromine liquid element Silver solid element

Classification of elements by state

– Elements are classified as metals and non-metals, depending on how well they conduct electricity and heat.

– Metals are good conductors and Non-metal very poor electrical conductors.

– Some elements are classified as Metalloids (or semi-metals). Metalloids have properties between those of metals and non metals.

Noble gases

lead

mercury

copper

boron

silikon

carbon

chlorine neon

sulphur

metal Non - metalMetalloid

Classification of elements as metal and non metals

Properties Metals Non-metals

Ability to conduct heat and electricity

Good conductor Poor conductor (except carbon)

Densities, melting and boiling point

Usually solids (except

mercury), high densities, high melting points

and boiling points

Usually liquid and gases with low densities, low melting points

and boiling points

Appearance Usually hard and shiny

Usually soft and dull

Are they malleable?(mudah ditempa )

Yes No

Classification of elements as in the periodic table

What are elements made of?• Atoms

An atom is the smallest unit of an element, having properties of that element.

The atoms of one element are different from the atoms of any other element. For example, all hydrogen atoms are the same and are different from atoms of carbon or iron.

• Molecules Most gaseous elements form molecules

comprising two atoms. Example:– Oxygen (O2),

– Hydrogen (H2),

– Nitrogen (N2),

– Chlorine (Cl2)

N N+ N N

N2 Gases

Post test

Answer this question.• Define an element.• State the names and symbols of

some common elements.• Describe ways of classifying the

elements.

YOU CAN VISIT THIS WEBSITEwww.chem4kids.com

COMPOUND

• Compound is a substance containing two or more elements chemically joined together.

• Compound is a single matter that cannot be broken down by physical separation.

• The compound can only be broken down into its elements by a chemical reaction.

If elements combine together, they will completely change.

For example:Water (H2O) is a compound made up of Hydrogen

and Oxygen.

Hydrogen and Oxygen are colourless gases, and the compound water is colourless liquid

HH O HH O+

What are Compound made of?

Molecules is the smallest particle of a compound.

A compound contain only one kind of molecule.

Molecule is a group of two or more atoms chemically joined together.

The chemical formula for water is

This formula tells us that a water molecule contains 2 hydrogen atoms and 1 oxygen atom

CHEMICAL FORMULA OF A MOLECULE

The chemical formula of a molecule shows the number and kinds of atoms contained in it.

Symbol of atom

The amount of atoms present in

one molecule

H2O

1. State the number of atoms and name the kinds of atoms shown by each formula

a. Alcohol, C2H5OH

b. Refined sugar, C12H22O11

c. Sulphuric acid, H2SO4

d. Sulphur dioxide, SO2

e. Glucose, C2H12O6

f. Urea, CO (NH2)2

THINK TIME

Names of compound• Many compound contain a metal and a non-metal.

The metal part usually comes first, followed by the non-metal part. – For example: NaCl (sodium chloride)

• The names of many compounds with only two elements often end in –ide. – For example: MgO (magnesium oxide)

• If the name of compound end in –ate, they contain oxygen. – For example: CaCO3 (Calcium Carbonate)

• Acids are compounds. Their names usually end in –ic acid. – For example: HCl (Hidrochloric acid)

These are some of the chemical formulaCompound Chemical Formula

Sodium Chloride NaCl

Magnesium Oxide MgO

Sodium hydroxide NaOH

Calcium carbonate CaCO3

Sulphuric acid H2SO4

Water H2O

Ammonia NH3

Carbon dioxide CO2

Sucrose (sugar) C12H22O11

1. Calculate the comparison between the mass of hydrogen and oxygen in water compound. What is the result?

2. What will happen if the mass of hydrogen and oxygen reacting does not follow the comparison?

3. What can you conclude about the comparison of elements in the compound?

No

BEFORE REACTION AFTER REACTION

Hydrogen Oxygen Water produced Excess

1 1 gram 8 gram 9 gram None

2 2 gram 16 gram 18 gram None

3 2 gram 8 gram 9 gram 1 gram of hydrogen

4 2 gram 17 gram 18 gram 1 gram of oxygen

5 3 gram 30 gram 27 gram 6 gram of oxygen

Chemical reaction between hydrogen and oxygen producing water

Conclusiona. Water was compound by hydrogen

and oxygen with ratio of 1:8 (1 for hydrogen and 8 for oxygen)

b. If the ratio of H:O was not equal to 1:8, there would be an excess element (sisa)

c. The mass of elements before and after a reaction was CONSTANT

PROUST’S LAW“The mass ratio of elements of a

compound component is constant”

(Perbandingan massa unsur-unsur penyusun senyawa adalah tetap)

Think Time1. When 4 grams of hydrogen react with 16 grams of

oxygen, how many grams of water are produced? If there is an excess, determine the element and it mass

Answer:• The comparison for the mass of

hydrogen and oxygen is 1:8No

Before reaction After reaction

Hydrogen Oxygen Water produced Excess

1 4 gram 16 gram 18 gram(2 gram of hydrogen and 16 gram of oxygen)

2 gram of Hydrogen

Mixtures• In the world, there are many

things that’s not pure substances.• Mixtures consist of two or more

substances that are not chemically joined together.

• Mixtures can consist of elements, compound or both. Also the substances in a mixtures may be solids, liquids or gases

Sea water is mixture of compounds including water

and sodium chloride

Brass is a mixture of the elements copper and zinc

Classification of mixtures

The prefixes "homo"- indicate samenessA homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions.

Homogeneous

The prefixes: "hetero"- indicate difference.A heterogeneous mixture consists of visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid.

Heterogeneous

In sugar solution, sugar

is the solute and water is the

solvent

Compound Mixtures

Composition Has a fixed composition by mass

Has a variable composition by mass

Melting and Boiling point

Has fixed melting and boiling points

Has variable melting and boiling points

Properties Has it own properties which are different from its elements

Does not usually have its own properties; it has the same properties as its component

Separation Cannot be separated by physical means. Chemical reaction is needed to separate the elements

Can be easily separated into its components by physical means.

Differences between compound and mixtures

Identify each of the following diagrams as an atom, molecule, element, compound or mixture.