SCIENCE

🔬 SCIENCE REVIEWER

Atomic Models • Atoms • Matter • KMT • Scientific Investigation • Solutions • Acids & Bases • Cells • Microscope

PART I — ATOMIC MODELS AND ATOMS

1. Scientific Models

A scientific model is a representation of an object, system, process, or idea that helps scientists understand and explain something that may be difficult to observe directly.

Scientific models can be changed or improved when new evidence becomes available.

Important Atomic Models

1. Dalton’s Atomic Model

Scientist: John Dalton

• Atoms were described as solid, indivisible spheres.

• Atoms of the same element were thought to be identical.

• Different elements have different types of atoms.

• Atoms combine in specific ratios to form compounds.

Visual idea: ⚫ Solid ball

Remember:

Dalton → Solid Sphere

2. Thomson’s Plum Pudding Model

Scientist: J. J. Thomson

• Thomson discovered the electron.

• The atom was described as a positively charged sphere containing negatively charged electrons.

• Electrons were embedded throughout the positive material.

Visual idea: A positive sphere with electrons scattered throughout it.

Remember:

Thomson → Plum Pudding → Electron

3. Rutherford’s Nuclear Model

Scientist: Ernest Rutherford

Based on the gold foil experiment.

• The atom is mostly empty space.

• It contains a small, dense, positively charged nucleus.

• Most of the atom’s mass is concentrated in the nucleus.

• Electrons occupy the space around the nucleus.

Remember:

Rutherford → Nucleus → Mostly Empty Space

4. Bohr’s Atomic Model

Scientist: Niels Bohr

• Electrons move around the nucleus in specific energy levels or shells.

• Electrons can move between energy levels by gaining or losing energy.

Remember:

Bohr → Energy Levels

5. Modern/Quantum Mechanical Model

The modern atomic model describes electrons as existing in regions of probability called orbitals.

Electrons are not treated as traveling in fixed circular paths like planets.

Remember:

Modern Model → Electron Cloud/Orbitals

⭐ Atomic Model Memory Trick

Dalton → Solid Sphere

Thomson → Plum Pudding → Electron

Rutherford → Nucleus

Bohr → Energy Levels

Modern → Electron Cloud/Orbitals

2. Atoms

An atom is the smallest unit of an element that retains the chemical identity of that element.

Atoms are made of three major subatomic particles.

Easy Memory:

Proton = Positive

Neutron = Neutral

Electron = Negative

Nucleus

The nucleus is the small, dense center of an atom.

It contains:

• Protons

• Neutrons

Most of the atom’s mass is found in the nucleus.

Atomic Number

The atomic number is the number of protons in an atom.

Atomic Number = Number of Protons

For a neutral atom:

Number of Protons = Number of Electrons

Mass Number

The mass number is the total number of protons and neutrons.

Mass Number = Protons + Neutrons

Therefore:

Neutrons = Mass Number − Atomic Number

PART II — MATTER AND PARTICLES

3. Matter

Matter is anything that has mass and occupies space.

Examples:

• Water

• Air

• Rocks

• Plants

• Animals

• Your body

Matter is made up of tiny particles.

4. Particles

Particles are tiny units that make up matter.

The particles of matter are constantly moving.

The behavior of particles helps explain:

• States of matter

• Diffusion

• Temperature

• Changes of state

• Pressure

• Other properties of matter

5. Motion of Particles

Particles are always in motion.

Solid

Particles:

• Are closely packed.

• Vibrate around fixed positions.

• Have relatively strong attractions.

Liquid

Particles:

• Are close together.

• Can move or slide past one another.

• Have weaker attractions than solids.

Gas

Particles:

• Are far apart.

• Move freely and rapidly.

• Have relatively weak attractions.

⭐ Remember:

Solid → Vibrate

Liquid → Slide

Gas → Move freely

6. Diffusion

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration because of random particle motion.

Diffusion continues until particles become more evenly distributed.

Example:

When perfume is sprayed in one part of a room, its particles gradually spread throughout the room.

Factors That Affect Diffusion

• Temperature

• Particle size

• Concentration difference

• The medium through which particles move

⭐ Remember:

High concentration → Low concentration

7. Temperature

Temperature is a measure related to the average kinetic energy of particles in a substance.

When temperature increases:

• Particles generally move faster.

• Average kinetic energy increases.

When temperature decreases:

• Particles generally move more slowly.

• Average kinetic energy decreases.

Important:

Temperature is not the same as heat.

8. Space Between Particles

There is space between particles.

The amount of space varies between states of matter.

Solid

Very little space between particles.

Liquid

More space than solids.

Gas

Large spaces between particles.

This helps explain why gases can be compressed more easily than solids and liquids.

9. Attraction Between Particles

Particles exert attractive forces on one another.

Solid

Strong attraction

Particles stay close together.

Liquid

Moderate attraction

Particles stay relatively close but can move past one another.

Gas

Weak attraction

Particles are far apart and move freely.

⭐ Remember:

Solid = Strong

Liquid = Medium

Gas = Weak

10. Phases/States of Matter

Solid

• Definite shape

• Definite volume

• Particles closely packed

• Strong particle attraction

• Particles mainly vibrate in place

Liquid

• No definite shape

• Definite volume

• Takes the shape of its container

• Particles can move past one another

Gas

• No definite shape

• No definite volume

• Fills its container

• Particles are far apart

• Particles move freely

11. Changes of Phase

Melting

Solid → Liquid

Example: Ice → Water

Freezing

Liquid → Solid

Example: Water → Ice

Vaporization

Liquid → Gas

Includes:

• Evaporation

• Boiling

Condensation

Gas → Liquid

Example: Water vapor → Water droplets

Sublimation

Solid → Gas

Example: Dry ice changing directly into carbon dioxide gas.

Deposition

Gas → Solid

Example: Frost forming from water vapor.

⭐ Phase Change Memory

Melting: S → L

Freezing: L → S

Vaporization: L → G

Condensation: G → L

Sublimation: S → G

Deposition: G → S

12. Energy

Energy is the ability to cause change or do work.

Kinetic Energy

Energy associated with motion.

Particles have kinetic energy because they are constantly moving.

Potential Energy

Stored energy related to position or arrangement.

Thermal Energy

The total internal energy associated with the random motion and interactions of particles in a substance.

Remember:

Kinetic = Motion

Potential = Stored

PART III — KINETIC MOLECULAR THEORY

13. Kinetic Molecular Theory (KMT)

The Kinetic Molecular Theory explains the behavior of matter, especially gases, in terms of particles and their motion.

Main Ideas of KMT

1. Matter is made up of tiny particles.

2. Particles are in constant random motion.

3. There are spaces between particles.

4. Particles interact with one another.

5. Temperature is related to the average kinetic energy of particles.

6. In an ideal gas, particles have negligible volume compared with the space between them.

7. In an ideal gas, collisions between particles and container walls are considered elastic.

⭐ Most Important KMT Idea:

Higher temperature → Greater average kinetic energy → Faster particle motion

PART IV — PURE SUBSTANCES AND MIXTURES

14. Pure Substance

A pure substance has a fixed and uniform composition.

There are two major types:

Element

A pure substance made of only one type of atom.

Examples:

• Gold (Au)

• Oxygen (O₂)

• Iron (Fe)

• Carbon (C)

Compound

A pure substance made of two or more different elements chemically bonded together in fixed proportions.

Examples:

• Water (H₂O)

• Carbon dioxide (CO₂)

• Sodium chloride (NaCl)

⭐ Difference:

Element → One type of atom

Compound → Different elements chemically bonded

15. Solution

A solution is a homogeneous mixture in which one or more substances are evenly distributed throughout another substance.

Solute

The substance that is dissolved.

Solvent

The substance that dissolves the solute.

Example:

Salt + Water = Saltwater

Salt → Solute

Water → Solvent

⭐ Memory:

Solute = Gets dissolved

Solvent = Does the dissolving

PART V — ACIDS AND BASES

16. Acid

An acid is a substance that produces hydrogen ions (H⁺) in aqueous solution.

Common properties:

• pH less than 7

• Often sour in taste

• Can react with certain metals

• Turns blue litmus paper red

Examples:

• Hydrochloric acid

• Acetic acid

• Citric acid

⚠ Never taste an unknown substance to determine whether it is acidic.

17. Base

A base is a substance that can accept hydrogen ions or produce hydroxide ions (OH⁻) in aqueous solution.

Common properties:

• pH greater than 7

• Many bases feel slippery

• Turns red litmus paper blue

• Can neutralize acids

Examples:

• Sodium hydroxide

• Calcium hydroxide

• Ammonia solution

18. pH Scale

The pH scale is used to describe how acidic or basic an aqueous solution is.

Acidic → pH < 7

Neutral → pH ≈ 7

Basic → pH > 7

⭐ Easy Memory:

ACID = Below 7

NEUTRAL = 7

BASE = Above 7

PART VI — SCIENTIFIC INVESTIGATION

19. Scientific Investigation

A scientific investigation is a systematic process used to answer questions and obtain evidence through observation, measurement, experimentation, and analysis.

Parts of a Scientific Investigation

1. Question/Problem

What do you want to find out?

2. Research

Gather information about the topic.

3. Hypothesis

A testable prediction or possible explanation.

A common format:

If… then… because…

Example:

“If a plant receives more sunlight, then it will grow taller because sunlight provides energy needed for photosynthesis.”

4. Experiment

A controlled procedure used to test the hypothesis.

5. Data Collection

Record observations and measurements.

6. Data Analysis

Examine and interpret the collected data.

7. Conclusion

State what the evidence shows and whether the hypothesis was supported.

8. Communication

Share the results with others.

⭐ Scientific Investigation Order

Question → Research → Hypothesis → Experiment → Data → Analysis → Conclusion → Communication

20. Variables of an Experiment

Variables are factors that can change or be measured in an experiment.

Independent Variable

The factor that the researcher changes or manipulates.

Memory:

Independent = I change it

Dependent Variable

The factor that is measured or observed.

Memory:

Dependent = Data I measure

Controlled Variables

Factors that are kept the same throughout the experiment.

Memory:

Controlled = Constant

Example:

Question:

“How does the amount of sunlight affect plant growth?”

Independent variable: Amount of sunlight

Dependent variable: Plant growth/height

Controlled variables:

• Type of plant

• Amount of water

• Type of soil

• Pot size

• Amount of fertilizer

PART VII — CELLS

21. Cell

The cell is the basic structural and functional unit of life.

There are two major types of cells:

• Prokaryotic cells

• Eukaryotic cells

Prokaryotic

• No membrane-bound nucleus

• Simpler cell organization

• Example: Bacteria

Eukaryotic

• Has a membrane-bound nucleus

• More complex cell organization

• Examples: Plant and animal cells

22. Animal Cell

Animal cells are eukaryotic cells.

Important Organelles

Cell Membrane

Controls what enters and leaves the cell.

Cytoplasm

Jelly-like material where many cellular processes occur.

Nucleus

Contains most of the cell’s DNA and helps control cell activities.

Mitochondria

Site of cellular respiration and major ATP production.

Ribosomes

Make proteins.

Endoplasmic Reticulum (ER)

Helps make and transport proteins and lipids.

Golgi Apparatus

Modifies, sorts, and packages certain proteins and lipids.

Lysosomes

Contain enzymes that help break down materials and cellular waste.

Important:

Animal cells do not have a cell wall or chloroplasts.

23. Plant Cell

Plant cells are also eukaryotic cells.

They have many of the same organelles as animal cells but also contain structures important for plant life.

Important Organelles

Cell Wall

Provides support and protection.

Cell Membrane

Controls movement of substances into and out of the cell.

Nucleus

Contains most of the cell’s DNA.

Chloroplasts

Site of photosynthesis and contain chlorophyll.

Large Central Vacuole

Stores water and other substances and helps maintain pressure inside the cell.

Mitochondria

Site of cellular respiration.

Ribosomes

Make proteins.

24. Plant vs. Animal Cell

⭐ Easy Memory:

Plant = Wall + Chloroplast + Big Vacuole

PART VIII — BACTERIA

25. Bacteria

Bacteria are microscopic single-celled prokaryotic organisms.

Characteristics

• Usually unicellular

• Prokaryotic

• Do not have a membrane-bound nucleus

• DNA is located in a region called the nucleoid

• Have a cell membrane

• Most have a cell wall

• Do not have membrane-bound organelles such as mitochondria or chloroplasts

Helpful Bacteria

Some bacteria:

• Help decompose organic matter.

• Are used in food production.

• Live in or on organisms and may be beneficial.

Harmful Bacteria

Some bacteria:

• Cause diseases.

• Spoil food.

• Produce harmful substances.

⭐ Remember:

Bacteria = Unicellular + Prokaryotic

PART IX — UNICELLULAR AND MULTICELLULAR ORGANISMS

26. Unicellular Organisms

Unicellular means an organism is made up of one cell.

That single cell performs all necessary life processes.

Examples:

• Bacteria

• Many protists

• Some fungi, such as yeast

Memory:

Uni = One

27. Multicellular Organisms

Multicellular means an organism is made up of many cells.

Different cells can become specialized for different functions.

Examples:

• Humans

• Dogs

• Trees

• Most animals

• Most plants

Memory:

Multi = Many

28. Unicellular vs. Multicellular

PART X — MICROSCOPE

29. Microscope

A microscope is an instrument used to magnify and observe objects that are too small to be seen clearly with the naked eye.

A common type used in schools is the compound light microscope.

30. Parts of a Microscope

31. Objective Lenses

Scanning Objective

Usually 4×.

• Lowest magnification

• Widest field of view

• Used to locate the specimen

Low-Power Objective

Usually 10×.

• Provides greater magnification than scanning

High-Power Objective

Usually 40×.

• Provides a more detailed view

Oil-Immersion Objective

Often 100×.

• Used with immersion oil

• Provides very high magnification

• Common in more advanced laboratory work

32. Total Magnification

To calculate total magnification:

Total Magnification = Eyepiece Magnification × Objective Magnification

Example:

Eyepiece = 10×

Objective = 40×

10 × 40 = 400×

Therefore:

Total Magnification = 400×

33. Coarse vs. Fine Adjustment

Coarse Adjustment Knob

• Makes large adjustments.

• Used for rough/initial focusing.

• Mainly used with low-power objectives.

Fine Adjustment Knob

• Makes small adjustments.

• Used to make the image sharp and clear.

• Especially important at higher magnifications.

⭐ Remember:

Coarse = Big/Rough adjustment

Fine = Small/Precise adjustment

34. Proper Microscope Handling

1. Carry the microscope with two hands.

2. Hold the arm with one hand.

3. Support the base with the other hand.

4. Place it gently on a stable, flat surface.

5. Start with the lowest-power objective.

6. Use the coarse adjustment for initial focusing on low power.

7. Use the fine adjustment for precise focusing.

8. Never touch the lenses with your fingers.

9. Clean lenses using proper lens paper.

10. After use, return the microscope to the lowest-power objective.

11. Turn off the light source.

12. Store the microscope properly.

🧠 SUPER QUICK MASTER REVIEW

ATOMIC MODELS

Dalton → Solid Sphere

Thomson → Plum Pudding → Electron

Rutherford → Nucleus → Empty Space

Bohr → Energy Levels

Modern → Electron Cloud/Orbitals

ATOM

Proton → + → Nucleus

Neutron → 0 → Nucleus

Electron → − → Outside Nucleus

Atomic Number = Protons

Mass Number = Protons + Neutrons

MATTER

Matter = Has Mass + Occupies Space

Solid → Closely packed + Vibrate

Liquid → Close + Slide

Gas → Far apart + Move freely

DIFFUSION

High concentration → Low concentration

TEMPERATURE

Higher temperature → Higher average kinetic energy → Faster particle motion

PARTICLE ATTRACTION

Solid → Strong

Liquid → Moderate

Gas → Weak

PHASE CHANGES

Melting: S → L

Freezing: L → S

Vaporization: L → G

Condensation: G → L

Sublimation: S → G

Deposition: G → S

PURE SUBSTANCES

Element → One type of atom

Compound → Different elements chemically bonded

SOLUTION

Solute → Gets dissolved

Solvent → Does the dissolving

ACID & BASE

Acid → pH < 7

Neutral → pH ≈ 7

Base → pH > 7

SCIENTIFIC INVESTIGATION

Question → Research → Hypothesis → Experiment → Data → Analysis → Conclusion → Communication

VARIABLES

Independent → I change it

Dependent → I measure it

Controlled → Keep it the same

CELLS

Plant = Cell Wall + Chloroplast + Large Central Vacuole

Animal = No Cell Wall + No Chloroplast

Bacteria = Unicellular + Prokaryotic

ORGANIZATION

Unicellular = One Cell

Multicellular = Many Cells

MICROSCOPE

Eyepiece → Look through it

Objective → Magnifies

Nosepiece → Changes objective

Stage → Holds slide

Stage Clips → Hold slide

Diaphragm → Controls light

Condenser → Concentrates light

Coarse → Rough focus

Fine → Sharp focus

Arm → Supports/helps carry

Base → Supports microscope

⭐ TOP 20 THINGS TO MEMORIZE

1. Dalton = Solid sphere

2. Thomson = Plum pudding/electron

3. Rutherford = Nucleus

4. Bohr = Energy levels

5. Proton = +

6. Neutron = 0

7. Electron = −

8. Atomic number = Number of protons

9. Diffusion = High → Low concentration

10. Higher temperature = Faster average particle motion

11. Solid → Liquid → Gas = Increasing particle freedom

12. Element = One type of atom

13. Compound = Different elements chemically bonded

14. Solute = Dissolved; Solvent = Dissolves

15. Acid < 7; Neutral ≈ 7; Base > 7

16. Independent = Changed; Dependent = Measured; Controlled = Constant

17. Plant cell = Cell wall + Chloroplast + Large central vacuole

18. Bacteria = Prokaryotic + Usually unicellular

19. Uni = One; Multi = Many

20. Total magnification = Eyepiece × Objective