Science U2+3 + Working Scientifically

What is an atom?

The smallest unit of an element that keeps its properties.

An atom’s structure

protons determine which element it is; electrons determine how it interacts

An atom’s structure: protons

determine which element it is.

An atom’s structure: electrons

determine how it interacts

An atom’s structure: neutrons

contribute to its stability.

What is the charge of an electron?

Negative

What is the charge of a proton?

Positive

What is the charge of a neutron?

Neutral (0 charge)

Where are protons and neutrons located in an atom?

In the nucleus

Where are electrons located in an atom?

In the electron cloud

Electron shell capacities

K shell: 2; L shell: 8; M shell: 18

Electron shell capacity: K shell

2

Electron shell capacity: L shell

8

Electron shell capacity: M shell

18

What does the Billiard Ball Model (Dalton’s model) suggest about atoms?

Atoms are tiny, uniformly dense, hard, indivisible spheres.

What evidence supported the Billiard Ball Model?

The Law of Conservation of Mass — mass is unchanged in a chemical reaction, showing particles are rearranged, not created or destroyed.

What did Rutherford’s Gold Foil Experiment show?

Most alpha particles passed straight through; a few bounced back — showing a small, dense, positively charged nucleus.

Rutherford’s model

nucleus made only of protons; electrons move randomly around it.

Rutherford’s model: nucleus

made only of protons (positive charge).

Rutherford’s model: electrons

randomly moving around the nucleus.

What evidence supported Bohr’s model of the atom?

Light spectroscopy showed electrons move between fixed energy levels.

What does Bohr’s model of the atom suggest?

A nucleus of protons; electrons orbit in fixed paths.

Bohr’s model: nucleus

made of only protons.

Bohr’s model: electrons

orbit in fixed paths.

What does the atomic number represent?

Number of protons (equal to electrons in a neutral atom).

Periodic table structure

periods = electron shells; groups = valence electrons.

Periodic table: periods

equal the number of electron shells.

Periodic table: groups

equal the number of valence electrons.

How does atomic size change left → right?

It decreases.

How does atomic size change down a group?

It increases.

Where are elements most reactive?

Corners of the periodic table.

How does ionization energy change toward the top right?

It increases.

How does electron affinity change toward the top right?

It increases.

Where are the most metallic elements?

Bottom left.

Where are the most non‑metallic elements?

Top right.

Periodic trends summary

more reactive (corners); less atomic size (right); more atomic size (left); higher ionization energy (top right); higher electron affinity (top right); non‑metallic (top right); higher atomic radius (bottom left); metallic (bottom left)

Periodic trend: reactivity (corners)

→ More reactive

Periodic trend: atomic size (right)

→ Less atomic size

Periodic trend: atomic size (left)

→ More atomic size

Periodic trend: ionization energy (top right)

→ Higher Ionization Energy

Periodic trend: electron affinity (top right)

→ Higher Electron Affinity

Periodic trend: metallic character (top right)

→ Non‑metallic

Periodic trend: atomic radius (bottom left)

→ Higher Atomic Radius

Periodic trend: metallic character (bottom left)

→ Metallic

In which direction do ionization energy and electron affinity increase?

Toward the top right.

Why is steel used in bridges and car frames?

Tightly packed atoms give high tensile strength.

Why is copper used in wiring?

Free electrons give excellent conductivity.

Why is rubber used in tyres and shock absorbers?

Long polymer chains stretch and return to shape, absorbing impact.

What is energy?

The ability to do work, measured in Joules (J).

What is force?

A push, pull, or twist, measured in Newtons (N).

What is potential energy?

Stored energy an object possesses.

What is kinetic energy?

Energy of motion.

Types of energy summary

gravitational; chemical; elastic; thermal

Types of energy: gravitational — description

Energy due to position in a gravitational field.

Types of energy: chemical — description

Energy stored in atomic

Types of energy: elastic — description

Energy stored when stretched or compressed.

Types of energy: thermal — description

Energy stored in particle motion.

Types of energy: gravitational — example

Book on a shelf.

Types of energy: chemical — example

Household battery.

Types of energy: elastic — example

Stretched rubber band.

Types of energy: thermal — example

Boiling water.

Types of energy: gravitational — PE

KE

Types of energy: chemical — PE

KE

Types of energy: elastic — PE

KE

Types of energy: thermal — PE

KE

State the Law of Conservation of Energy.

Energy cannot be created or destroyed, only transformed.

Heat transfer summary

conduction; convection; radiation

Heat transfer: conduction

Heat transfer through direct contact in solids.

Heat transfer: convection

Heat transfer through moving fluids.

Heat transfer: radiation

Heat transfer by electromagnetic waves.

Energy transformation: toaster

Electrical → thermal

Energy transformation: solar panel

Light → electrical

What is an open system?

Exchanges energy and matter (e.g. boiling pot).

What is a closed system?

Exchanges energy but not matter (e.g. pressure cooker).

What are reactants?

Substances present before a chemical reaction.

What are products?

Substances formed after a chemical reaction.

Signs of chemical change

formation of water; colour change; gas production; temperature change; precipitate formed

Signs of chemical change: formation of water

Appearance of water droplets.

Signs of chemical change: colour change

Permanent colour change indicates new substance.

Signs of chemical change: gas production

Bubbles or fizzing.

Signs of chemical change: temperature change

Substance absorbs or releases heat.

Signs of chemical change: precipitate formed

Insoluble solid forms.

Indicator of physical change

State change

What is an endothermic reaction?

Absorbs energy; surroundings get cooler (e.g. photosynthesis).

What is an exothermic reaction?

Releases energy; surroundings get warmer (e.g. campfire).

What does the Billiard Ball Model suggest?

A nucleus of protons; electrons flying randomly.

K-Shell

Up to 2 electrons.

L-Shell

Up to 8 electrons.

M-Shell

Up to 18 electrons.

Electron: mass, location, charge

0.00058 amu; electron cloud; 0 charge.

Proton: mass, location, charge

1.00727 amu; nucleus; + charge.

Neutron: mass, location, charge

1.0082 amu; nucleus; 0 charge.

Word equation

Reactant 1 + Reactant 2 = Product 1 + Product 2

What is a chemical change?

Reactants convert into new substances with different chemical properties.

Technologies summary

electron microscope; particle accelerator

Electron microscope

Uses electron beams to image inside atoms.

Electron microscope: purpose

Allows scientists to observe individual atoms.

Particle accelerator

Propels atoms to near light speed.