Key Concepts

Question 1

Formulae

Element

Element=substance made from atoms with the same number of protons in the nucleus.each element has its own chemical symbol 
-consists of one or two letters 
-starts with a capital letter
-has any other letters in lower case 
E.g mercury is Hg 

Compounds
Compound=consists of two or more different element chemically together

-The chemical formula for methane is CH(little 4 at the bottom)
*Each methane molecule has:
*One carbon atom(no number in the formula)
*Four hydrogen atoms(4 in the formula)
Atoms of two elements joined together
*(1+4)= 5 atoms in total

Atoms and molecules

Atom=smallest particle of an element that still has its chemical properties

Molecule=consists two or more atoms chemically joined together

Chemical formulae=most elements that are gases at room temperature exist as molecules with two or more atoms . They are shown by chemical formulae

Answer 1

What is an element 
What does each element 
 have 
Describe them 
What is a compound 
What does a compound consists describe  this 
What is an atom 
What is a molecule

Question 2

Equations

*chemical equations are used to model the changes that happens in chemical reactions

Word equations

In a chemical reaction:

• reactants =substances that’s undergo a chemical change in a reaction
• products =new substances formed

In general:reactants(arrow) products

• two or more reactants/products are by a + sign
• in a word equation=write the name of each substance , not it’s formulae

Balanced equation

• all substances are shown by their formulae
• numbers of atoms of each element in the reactions and products are the same
• you may need to write in front of a reactant to Balance an equation

Answer 2

What chemical equations show
What is a reactant
What is a product what is a balanced equations
What is a unbalanced equation

Question 3

Hazards, risks and precautions

Hazards:

hazard =is something that could cause
-damage/harm to someone or something
-negative health effects ,which may occur immediately or later on
E.g ethanol is flammable this is a hazard . If ethanol is ignited it could cause burns or a fire

Risk =chance that someone or something will be harmed if exposed to a hazard
The amount of risk depends on factors such as:
-How much someone is exposed to a hazard
-The way in which exposure happens
-How serious the effects using a hot water bath is less than when using a Bunsen burner
*the risk from heating ethanol using a hot water bath is less than when using a Bunsen burner

Hazard symbol=labels on containers of hazardous substances
That’s are intended to:
-warn about the dangers of the substance in the container
-let people know about the precautions to take when they use the substance

Precaution
=something that you can do to reduce the risk of harm from a hazard
Precautions include:
-using smaller amounts of a hazardous substance
-using protective clothing , such as gloves and eye protection
-using a different method or apparatus

Answer 3

What is a hazard
What do hazard symbols intend to do 
What is a precaution
What is a risk
What are some commons hazard symbols 
She are the advantages of risks

Question 4

Atomic structure

*Daltons model has changed overtime because of the discovery of subatomic particles

Atomic timeline
1803-Dalton-solid atom model:all atoms of an element are identical;different elements have different atoms

1897-Thompson-discovers the electron

1904-Thomson -plum pudding model:atoms are spheres of positive charge with negative electrons dotted Around inside

1911-Rutherford -solar system model:atoms have a positive nucleus surrounded by negative electrons in orbits

1913-Bohr -electron shell model :electrons occupy shells or energy levels around the nucleus

1918-Rutherford-discovers the proton

1932-Chadwick-discovers the neutron

Atomic structure

Atom consists of s central nucleus, which:

• contains protons and neutrons
• is surrounded by electrons in shells

Answer 4

What happened to Daltons simple model
Describe the atomic brief timeline

What does the atom consists of . Describe it
How do you calculate relative mass

Question 5

Isoptopes

*Atoms of an element have identical chemical properties , but can exist as different isotopes

Numbers of particles

• each atom can be described by its:
• mass number ,,total number of protons and neutrons in the nucleus

-atomic number,the number of protons in the nucleus

Atoms of a given element have the same number of protons in the nucleus:

• all have the same atomic number
• this number is unique to that element

Isotopes
=are atoms of an element with:
-same number of pitons 
-different numbers of neutrons 
*You can recognise isoptopes of the same element because they will have the same atomic number , but different mass numbers 

*isotopes of an element have the same chemical properties because they have the same number of electrons

Relative atomic mass

Answer 5

What is an isotope 
What is a mass number 
What is an atomic number 
What is an isotope 
What is a relative atomic mass 
How do you calculate number particles

Question 6

The periodic table
Modern Periodic table = useful for describing and predicting properties and elements

Atomic number

In Mendeleev’s periodic table , atomic number was just the position of an element in the table.

Later discoveries showed that:

• atomic number is actually the number of protons in the nucleus of an atom
• each element has a unique atomic number
• if the elements are arranged in order of increasing atomic number , Mendeleev’s pair reversals are explained

Explaining pair reversal:

Iodine should be placed before tellurium according to its relative atomic mass , but after
tellurium its atomic number:

*mendeleev did not know about atomic structure . He could explain the pair reversal only in terms of the elements properties

Answer 6

What is the periodic table 
What is it useful for 
What is an Atomic number 
What did the discoveries show 
What is pair reversals 
What did Mendeleev not know 
What could he explain only

Question 7

Electric configuration
=describes the arrangement of electrons in shells in an atom

Modeling the arrangement of electrons
In an atom:
-electron occupy electron shell
-shells are filled , starting with the internist of electrons
-different shells hold different maximum of electrons

*diagrams show electron configuration e.g. Sodium which has 11 extrinsic in its atoms or 2.8.1( dots seperates two occupied shells a

Cation
=a positively Charged ion and formed when an atom or group of atoms loses one or more electrons

Cations usually form:

• group 1 atoms lose 1 electron to form ions with one positive charge(+)
• group 2 atom loses 2 electrons to form ions oh two positive charges (2+)

Anions
=negatively charged ion and formed when an atom or group of atoms gain one or more electrons

Anions usually form from non-metals:

• group 7 atoms gain 1 electron to form ions with one negative charge
• group 6 atoms gain 2 electrons to form ions with two negative charges (2-)
• In 2d models of 3D objects each dot/cross represent an electron
• Electrons are 3D

Answer 7

What is electric configuration

Describe in an atom modeling the arrangement of electrons
What is an ion
What is a cation
What is an ion
What do cations form
What do anions form
What do 2d models of 3D objects represent