Grade 9 Chemistry

What is matter?

Anything that has mass and takes up space.

What are the tiny particles that make up matter?

Atoms and molecules.

List the 6 main points of the Particle Theory of Matter.

1. All matter is made of tiny particles. 2. All particles in a pure substance are the same. 3. There are spaces between particles. 4. Particles are always moving. 5. Particles move faster when heated. 6. Particles attract each other.

What are the 3 main states of matter?

Solid, liquid, and gas.

Describe the particles in a solid.

Packed tightly, vibrate in place, fixed shape and volume.

Describe the particles in a liquid.

Close together but slide past each other, fixed volume, takes shape of container.

Describe the particles in a gas.

Far apart, move freely, no fixed shape or volume.

What are the two main classifications of matter?

Pure substances and mixtures.

What is a pure substance?

A substance made of only one type of particle.

What is an element?

A pure substance made of one type of atom.

What is a compound?

A pure substance made of two or more elements chemically combined.

What is a mixture?

Two or more substances physically combined, not chemically bonded.

What is a homogeneous mixture (solution)?

A mixture that looks uniform throughout (e.g., salt water).

What is a heterogeneous mixture (mechanical mixture)?

A mixture where different parts are visible (e.g., cereal in milk).

What is a suspension?

A cloudy mixture that separates over time (e.g., muddy water).

What is a physical property?

A characteristic that can be observed without changing the substance.

Give examples of physical properties.

Color, odor, state, hardness, luster, malleability, ductility, solubility, density, melting and boiling points.

What is a chemical property?

A characteristic that describes how a substance reacts with others.

Give examples of chemical properties.

Reactivity, combustibility, flammability, ability to rust, reaction with acid or water.

What is a physical change?

A change in appearance or state but no new substance forms.

What is a chemical change?

A new substance with new properties forms.

List the 6 indicators of a chemical change.

1. Color change 2. Gas produced 3. New odor 4. Precipitate forms 5. Energy released (heat/light/sound) 6. Energy absorbed (temperature drop).

If a new substance forms, what type of change occurred?

Chemical change.

What are metals?

Shiny, malleable, ductile, good conductors of heat and electricity.

What are nonmetals?

Dull, brittle, poor conductors.

What are metalloids?

Elements with properties of both metals and nonmetals.

What are the three subatomic particles in an atom?

Proton, neutron, and electron.

Where are protons located?

In the nucleus.

Where are neutrons located?

In the nucleus.

Where are electrons located?

In shells (energy levels) around the nucleus.

What is the charge of a proton?

Positive (+).

What is the charge of a neutron?

Neutral (0).

What is the charge of an electron?

Negative (−).

What is the nucleus made of?

Protons and neutrons.

What is the overall charge of a nucleus?

Positive.

What is the atomic number?

The number of protons in an atom.

What does the atomic number also equal?

The number of electrons.

What is the mass number?

The total number of protons and neutrons.

How do you calculate the number of neutrons?

Mass number − atomic number.

Why are atoms neutral?

Because they have equal numbers of protons and electrons.

How many electrons fit in the first shell?

2.

How many electrons fit in the second and third shells (for first 20 elements)?

8.

What are valence electrons?

Electrons in the outermost shell.

What is a cation?

A positively charged ion (lost electrons).

What is an anion?

A negatively charged ion (gained electrons).

What is an ion?

An atom that has gained or lost electrons and now has a charge.

What is an ionic charge?

The charge on an ion after losing or gaining electrons.

What is a compound?

A pure substance made of two or more elements chemically bonded.

What is an ionic compound?

A compound formed between a metal and a nonmetal by electron transfer.

What is a covalent (molecular) compound?

A compound formed between two or more nonmetals by sharing electrons.

What type of elements form ionic compounds?

Metals and nonmetals.

What type of elements form molecular compounds?

Nonmetals only.

What holds ionic compounds together?

The electrostatic attraction between positive and negative ions.

What holds molecular compounds together?

Shared pairs of electrons (covalent bonds).

List properties of ionic compounds.

Solid at room temp, hard, brittle, high melting/boiling points, conduct electricity when dissolved.

List properties of molecular compounds.

Can be solid/liquid/gas, low melting/boiling points, poor conductors, often not soluble in water.

What is the crisscross rule?

Cross the ionic charges to make subscripts in the formula.

What order are elements written in an ionic compound?

Metal first, nonmetal second.

How do you name an ionic compound?

Metal name + nonmetal name ending in “-ide.”

How do you name a compound with a multivalent metal?

Use Roman numerals to show the charge (ex. Iron (III) chloride).

What does “multivalent” mean?

A metal with more than one possible ionic charge.

What is a binary compound?

A compound containing only two different elements.

What is a molecular formula?

Shows the type and number of atoms in a compound (ex. H₂O, CO₂).

What are the prefixes used in molecular naming?

Mono (1), Di (2), Tri (3), Tetra (4), Penta (5).

How do you name molecular compounds?

Use prefixes + end the second element in “-ide.”

What is the difference between ionic and molecular naming?

Ionic uses no prefixes, molecular uses prefixes.

What is H₂O called?

Water (not dihydrogen oxide).

What is NH₃ called?

Ammonia (not nitrogen trihydride).

What does a subscript show?

The number of atoms of that element in one molecule.

What does a coefficient show?

The number of molecules of the compound.

What happens when a subscript is outside brackets?

It multiplies everything inside the brackets.

Example: How many atoms in 3O₂?

6 oxygen atoms.

Example: How many atoms in Mg(OH)₂?

1 magnesium, 2 oxygen, 2 hydrogen.

What does the Period number tell you?

The number of electron shells.

What does the Group number tell you?

The number of valence electrons.

How many periods are there on the periodic table?

7.

How many groups are there?

18.

List the main element families.

Alkali metals, alkaline earth metals, transition metals, lanthanides, actinides, metalloids, nonmetals, halogens, noble gases.

What are alkali metals like?

Very reactive, soft, 1 valence electron.

What are alkaline earth metals like?

Reactive metals, 2 valence electrons.

What are halogens like?

Very reactive nonmetals, 7 valence electrons.

What are noble gases like?

Unreactive, stable, full outer shell.

How does reactivity change across the table?

Metals become more reactive down a group, nonmetals more reactive up a group.

Which gases are unreactive?

Noble gases.

What is valency?

The number of electrons an atom must gain, lose, or share to achieve a full shell.

What is oxidation number?

The charge an atom would have if the bond was 100% ionic.

What is density?

Mass divided by volume.

Which has more density: 1 kg of paper or 1 kg of concrete?

They have the same mass, but concrete is denser because it takes up less volume.

If a sample has unique melting point, color, hardness, and boiling point, what is it?

An element.

What is a reactive material?

A substance that easily reacts with others.

What is an inert material?

A substance that does not easily react.

What does a Bohr-Rutherford diagram show?

Protons, neutrons, and electrons in energy shells.

What does a Lewis dot diagram show?

Only valence electrons around the element symbol.

What are covalent bonds?

Bonds formed when atoms share electrons.

What are ionic bonds?

Bonds formed when electrons are transferred.

What is the difference between a molecule and a compound?

A molecule is two or more atoms bonded, a compound is two or more different elements bonded.

Why are noble gases stable?

Because they have full outer shells.

What happens when energy is released in a reaction?

The reaction is exothermic.

What happens when energy is absorbed?

The reaction is endothermic.

Why are chemical tests used?

To identify substances by how they react.