Chemistry Year 9

Atom

a single neutrally charged particle of an element

Element

all atoms present are the same type

Pure element

A material made up of only one kind of atom, having the same number of protons in each atom

Molecule

a small cluster of atoms chemically bonded together which can consist of the same or different elements.

Compound

two or more types of atoms chemically bonded together to form a new substance with distinct properties.

Lattice

geometrical arrangements of atoms. Can be of similar or different alternating elements

Mixture

different elements or compounds combined together without chemically bonding

Subatomic particles

the particles inside an atom

proton

a positively charged subatomic particle located in the nucleus

Electron

a negatively charged subatomic particle that orbits the nucleus of an atom

Neutron

a subatomic particle of about the same mass as a proton but without an electric charge

Atomic Number

The number of protons in an atom

Mass Number

The total mass of an atom, determined by the sum of its protons and neutrons.

Electrically Neutral

an atom molecule or compound with a net charge of zero, resulting from an equal number of protons and electrons

Ion

An atom or molecule with a net electric charge due to the loss or gain of one or more electrons

Positive Ion

Cations are positively charged ions due to the loss of electrons, (occurs with outer shell of 1 2 3)

Negative ion

Anions are negatively charged ions due to the gain of electrons, the name of the ion ends with ide and occurs with outer shell of 5 6 7

Isotope

Elements with teh same atomic number but different masses

Electron shell

the energy levels or orbits around a nucleus where electrons are found, arranged in lowest to highest energy

Valence shell

the outermost electron shell of an atom

Half life

the amount of time for half of a sample of a radioactive element to decay into something else

Chemical change

result or observation of a chemical reaction

Chemical reactions

take place when the bonds between atoms break or new bonds are formed, creating a new arrangement of atoms and at least one new substance. No new atoms or elements are made only rearranged

Physical change

alters the form, appearance or state of matter without creating a new substance or changing its identity

Evidence of a chemical reaction

Permanent colour change, gas produced (not by heat), change in temp, formation of a precipitate, light is emitted, change in physical properties:melting, boiling point, electric conduct, volume

Precipitate

cause a substance to be deposited in solid form from a solution

Reactant

the substances you start with

Products

the substances formed

Exothermic

heat energy exits the system

endothermic

heat energy is absorbed, making surroundings cold

Chemical equation

a representation of a chemical reaction using formulas and symbols to show the conversion or reactants into products

Word equation

representation of a chemical reaction using the names of substances

Law of Conservation of Mass

atoms are neither created or destroyed only rearranged in a chemical equation

unbalanced

a reaction where the number of atoms for each element is not equal on both the reactant and product sides

balanced

the same number and type of atoms for each element are present on both the reactant and product sides

symbol

1 or 2 letters that belong to an element

subscripts

tell us how many of each atom are present (the small numbers)

subscript outside of bracket

can be expanded on to elements inside bracket

coefficients

multiply everything by that number, means multiple separate groups

nuclear number

the symbol for the element with the atomic number written on the bottom left and the mass number written on the top left

radiation

particles or energy released from a nucleus during radioactive decay

radioactive decay

the spontaneous disintegration of a nucleus into a smaller nucleus

radioisotopes

isotopes of the same element that have different numbers of neutrons and unstable nuclei

Why do some atoms decay?

their nuclei are unstable due to an unbalanced ratio of protons and neutrons or excessive size causing them to release energy and particles to reach a more stable state.

Alpha

Release of 2 protons and 2 neutrons, largest and slowest, least penetrating stopped by paper

Beta

Decay of a neutron into a proton and electron, electron is emitted into nucleus, stopped by aluminium foil

Gamma

not a particle, electromagnetic wave with short wavelength and high frequency and energy, no mass, no charge, very fast (speed of light), stopped by several cm of lead.

What is used to measure radiation

geiger counter, produces electric current when near radiation, results in clicks or a digital reading, may be recorded as counts per minute

Electronic Configuration

number of electrons in each shell

Rules for filling shells

each shell hasa limit, fill shells of lowest energy first, maximum of valence electrons is 8

Electron shell capacity

2n² - n = shell number

Periodic table

118 elements, smallest to largest, arranged according to similarities in their physical and chemical properties

groups

same number of outer shell electrons

periods

elements with the same number of electron shells

Alkali metals

group 1

alkali earth metals

group 2

transition metals

groups 3-12

halogens

group 17

noble gases

group 18

Ionic compounds

a chemical substance composed of positively charged ion and negatively charged ions

Ionic bonds

formed between metals or non-metals and oppositely charged ions, in the form of crystal lattices. Formed when one atom completely tranfers one or more valence electrons to another,

Group 1

1+

Group 2

2+

Group 13

3+

Group 15

3-

Group 16

2-

Group 17

1-

Flame Test

When heat is given to an atom electrons go from ground state (lowest possible energy levels) to excited state and enter a higher energy level. The higher energy level is not a stable position for the electron so it almost immediately returns to its ground state. When doing this is gives off excess energy usually in the form of light.

What is a chemical reaction?

A chemical reaction occurs when bonds between atoms are broken or new bonds are formed, producing at least one new substance.

What happens to atoms during a chemical reaction?

Atoms are rearranged. No new atoms or elements are created. At least one new substance is formed.

How is a chemical reaction different from a physical change?

Chemical reaction: New substance formed. Physical change: No new substance formed; only state or appearance changes.

What are the signs that a chemical reaction has occurred?

Permanent colour change, gas produced, temperature change, formation of a precipitate, light emitted, change in physical properties.

What is a precipitate?

A precipitate is a solid formed when two liquids react.

Does mixing two chemicals always cause a reaction?

No. Many reactions need energy to start.

What is activation energy?

The initial energy needed to start a chemical reaction.

What can provide activation energy?

Heat from surroundings, electric current, light, Bunsen burner flame.

What is an exothermic reaction?

An exothermic reaction releases energy to the surroundings. Heat energy EXITS the system.

Which has more energy in an exothermic reaction: reactants or products?

The reactants have more energy than the products.

What forms of energy are released in an exothermic reaction?

Usually: Heat, Light.

Why is energy released in an exothermic reaction?

The products store less energy in their chemical bonds than the reactants.

Give an example of an exothermic reaction.

Portable hand warmers: Iron, water, salt, and sawdust react. Heat is released. The pack becomes warm.

Memory trick for exothermic reactions

EXO = EXIT. Heat energy exits the system.

What is an endothermic reaction?

An endothermic reaction absorbs energy from the surroundings. Heat energy ENTERS the system.

Which has more energy in an endothermic reaction: reactants or products?

The products have more energy than the reactants.

Why is energy absorbed in an endothermic reaction?

The products store more energy in their chemical bonds than the reactants.

Where does an endothermic reaction get its energy from?

From the surroundings.

Give an example of an endothermic reaction.

Instant cold packs: Ammonium nitrate dissolves in water. Heat is absorbed from the surroundings. The pack becomes cold.

Memory trick for endothermic reactions

ENDO = ENTER. Heat energy enters the system.

Exothermic vs Endothermic Reactions

Exothermic: Heat exits system, energy released, reactants have more energy, surroundings get warmer. Endothermic: Heat enters system, energy absorbed, products have more energy, surroundings get cooler.

Key facts about exothermic and endothermic reactions

Exothermic: Energy released → surroundings warm up. Endothermic: Energy absorbed → surroundings cool down. Both require activation energy to begin.