G3 Science – Chapters 3, 4 & 8 Review

These question-and-answer flashcards cover the essential definitions, facts and processes from Chapters 3 (Chemical Composition), 4 (Separation Techniques) and 8 (Atoms & Molecules) of the G3 Science notes. Use them to test your understanding of atomic structure, elements, compounds, mixtures, solutions, solubility, and key laboratory separation methods.

What is the smallest unit of an element that still possesses the properties of that element?

An atom

Name the three types of sub-atomic particles found in an atom.

Protons, neutrons and electrons

Which sub-atomic particle carries a +1 charge?

Proton

Which sub-atomic particle carries a –1 charge?

Electron

Which sub-atomic particle has no electric charge?

Neutron

Where are protons and neutrons located in an atom?

In the nucleus

Where are electrons found in an atom?

Moving around the nucleus in electron shells

State the relative mass of a proton and a neutron.

Both have a relative mass of 1

State the relative mass of an electron.

1⁄1840 (taken as almost zero)

Why is an atom electrically neutral?

Because it has an equal number of protons (+) and electrons (–)

What is meant by the proton (atomic) number?

The number of protons in an atom; it identifies the element

What is meant by the nucleon (mass) number?

The total number of protons and neutrons in an atom

Give the formula to calculate the number of neutrons in an atom.

Number of neutrons = nucleon number – proton number

How many electrons can the first electron shell hold?

A maximum of 2 electrons

How many electrons can each of the second and third shells hold (for the first 20 elements)?

A maximum of 8 electrons each

What is the name of the outermost electron shell?

The valence (outer) shell

Define valence electrons.

Electrons found in the valence shell

When drawing electron shells, in what order should electrons be placed after the first two?

North, South, East, West around the nucleus

Define a molecule.

Two or more atoms chemically combined

Differentiate between a molecule of an element and a molecule of a compound.

Element: atoms are the same element; Compound: atoms are of different elements

Define an element in terms of chemical composition.

A pure substance that cannot be broken down into simpler substances by chemical, physical or electrical methods

Define a compound.

A pure substance made of two or more elements chemically combined in a fixed proportion by mass

Define a mixture.

Two or more elements and/or compounds not chemically combined

Give two properties that differ between a compound and the elements forming it.

Boiling/melting point, chemical reactivity (any valid differences)

State whether energy change usually accompanies the formation of a mixture.

No significant energy change occurs

Can the constituents of a compound be separated by physical means?

No, they require chemical methods or electricity

Can the constituents of a mixture be separated by physical means?

Yes, by methods such as filtration, distillation, etc.

Define a solution.

A homogeneous mixture formed when one or more solutes dissolve completely in a solvent

Define a solute.

The substance that is dissolved by a solvent in a solution, typically present in a smaller amount.

Define a solvent.

The substance in which the solute dissolves in

What is the difference between a dilute and a concentrated solution?

Dilute: small amount of solute per solvent; Concentrated: large amount of solute per solvent

Define a saturated solution.

A solution containing the maximum amount of dissolved solute at a given temperature

State three factors that affect the rate of dissolving a solid in a liquid.

Surface area of solute, temperature of solvent, rate of stirring

Define solubility.

How well a solute dissolves in a fixed volume of a particular solvent at a specific temperature

How does temperature affect the solubility of solids in liquids?

Solubility of solids generally increases with increasing temperature

How does temperature affect the solubility of gases in liquids?

Solubility of gases decreases as temperature increases

Define a suspension.

A heterogeneous mixture containing large insoluble solid particles suspended in a liquid

State one visible property that distinguishes a suspension from a solution.

In a suspension the solid particles settle or float when left to stand; a solution remains clear

Which separation technique removes magnetic materials from non-magnetic ones?

Magnetic attraction

Which technique separates insoluble solid particles from a liquid using filter paper?

Filtration

In filtration, what is the name of the solid left on the filter paper?

Residue

In filtration, what is the name of the liquid that passes through the paper?

Filtrate

Which technique is used to obtain a soluble solid that does NOT decompose on strong heating?

Evaporation to dryness

Which technique is used to obtain a soluble solid that WOULD decompose on strong heating?

Crystallisation

Explain briefly how crystallisation works.

Heat solution until saturated, allow to cool; decreased solubility causes solute to form crystals

What is a saturated solution in the context of crystallisation?

One that contains the maximum amount of solute at that temperature

Which separation technique separates a pure solvent from a solution?

Simple distillation

Why is the thermometer bulb placed beside the side-arm of the distillation flask?

To measure the boiling point of the vapour that is actually being distilled

Why are boiling chips added during distillation?

To ensure smooth boiling and prevent bumping

From which direction should cooling water enter a condenser, and why?

At the bottom and exit at the top, so the jacket fills completely with cold water and maximum cooling is achieved

Which separation technique is used for miscible liquids with close boiling points?

Fractional distillation

What additional apparatus is needed for fractional distillation compared with simple distillation?

A fractionating column (often packed with glass beads) and a round-bottom flask

State one industrial use of fractional distillation.

Separation of crude oil into different fractions (any valid example acceptable)

How can you test if a substance collected by distillation is pure?

Check that it boils at a constant, fixed boiling point

Define a pure substance in terms of melting and boiling points.

A substance with fixed and constant melting and boiling points

What does the last digit of an element’s group number usually indicate?

The number of valence electrons

How many valence electrons does an element in Group 17 possess?

Seven

Write the electronic configuration of a lithium atom (proton number 3).

2,1

If an atom has proton number 15 and nucleon number 31, how many neutrons does it have?

16 neutrons (31 – 15)