[SHALOM] SECOND SEMESTER SCIENCE

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Why are atoms electrically neutral?

Equal number of protons and electrons

Which part contributes most to atomic mass?

Nucleus

Why don’t electrons fall into nucleus?

They exist in energy levels

Compare proton neutron electron mass

Proton neutron heavy electron very light

Which particle determines element identity?

Proton

Which particle can vary without changing element?

Neutron

Why is atomic number important?

Defines the element

What happens if proton number changes?

Element changes

Limitation of Thomson model?

No nucleus explained

What did Rutherford discover?

Dense central nucleus

What did Bohr explain?

Stable electron orbits

Why is modern model accurate?

Uses probability

Why is matter compressible?

Atoms have empty space

What does empty space imply?

Particles far apart

Why do atoms form molecules?

To become stable

What makes a compound different?

Different atoms combined

Why is water a compound?

Hydrogen and oxygen bonded

Why is chemical formula important?

Shows atom ratios

What does H2O represent?

2 hydrogen 1 oxygen

What forms an ion?

Gain or loss of electrons

Why do ions have charge?

Unequal protons and electrons

Why are sodium and magnesium different?

Different proton numbers

Why atoms of same element similar?

Same structure

In chemical reaction what are reactants converted into?

Products

How can reactions be represented?

Word equations

Ways to start reactions?

Heat light electricity mixing

What happens to mass in reaction?

Mass conserved

What is combination reaction?

Multiple reactants form one product

Example combination?

Water formation

What is decomposition?

Breakdown into simpler substances

Example decomposition?

Electrolysis of water

What is combustion?

Reaction with oxygen forming oxides

Example combustion?

Methane burning

Test for hydrogen?

Pop sound

Test for carbon dioxide?

Limewater turns milky

Difference physical chemical?

New substance forms only in chemical

Which change reversible?

Physical

Which change not reversible?

Chemical

What indicates chemical change?

New substance and energy change

What defines a fuel?

Releases energy when burned

Energy forms from fuels?

Heat and light

Why is petrol a fuel?

Provides energy for movement

Name fuels

Wood charcoal kerosene gas

Gas needed for burning?

Oxygen

Gas produced burning?

Carbon dioxide

Flame with air hole closed?

Luminous

Flame with air hole open?

Non luminous

Which flame hotter?

Non luminous

Which flame produces soot?

Luminous

Independent variable in flame test?

Type of flame

Why control variables?

Ensure fair test

How improve accuracy?

Repeat and average

Fossil fuels rich in?

Carbon hydrogen

Examples fossil fuels?

Coal oil gas

Why widely used?

High energy output

How used in power stations?

Produce steam for turbines

How coal formed?

Plants under heat pressure

How oil formed?

Plankton under pressure

How gas formed?

Decomposition

Main gas component?

Methane

Why non renewable?

Take millions of years

Environmental issue CO2?

Global warming

Gases causing acid rain?

Sulphur dioxide nitrogen oxides

Why conserve energy?

Reduce pollution and usage

Example conserve energy?

Switch off appliances