Elements & Physical/Chemical Properties (Yr_8) Flashcards
What are the main ideas of elements?
- one type of atom
- pure substance
- building blocks of the universe
- atoms within all have the same structure
- cannot be broken down into different elements
What are unstable elements?
- highly radioactive
- about 20
- too big to be stable
- breaks down immediately after being formed
Organising elements in the periodic table:
- organised in order of their atomic number
- created by Dimitri Mendeleev
- grouped according to similar properties
- horizontal periods
- vertical are groups
Atoms & properties
An element’s properties are determined by the nature of their atoms.
Different types of elements in the periodic table:
Metals on the left
Non-metals on the right
Metalloids in the middle with properties of both metals and non-metals
What is the atomic number determined by?
The amount of protons in the nucleus.
Element symbols:
Elements can be represented by symbols
one or two letters which usually relate to the element’s name
How are elements classified?
They are classified by their chemical properties aka. how they react with other substances
What are compounds?
Compounds are made up of two or more different elements that are chemically combined in a specific ratio.
Formulas
A formula is just a chemical shorthand for the compound.
The subset shows how many atoms are present.
What are molecules?
A molecules formed by two or more atoms
What are diatomic molecules?
Molecules formed by two of the same atom.
What are some physical properties?
Boiling/melting point
density
viscosity
malleability
conductivity
ductility
What are some chemical properties?
How reactive a chemical substance is
flammability
corrosiveness
toxicity
half life
vaporisation
How does arrangement of particles change?
Particles rearrange to change shape
Particles break and create bonds which could change state
How does reversibility change?
Physical changes are reversible
chemical changes are irreversible
How does conservation of mass change?
The mass normally doesn’t change.
Mass normally changes
How does energy change?
There are energy changes to change state, like water and ice
There are energy changes which break and create new bonds.
What is a physical change?
- does not change identity of substance
- change size, shape and mass
- different form
What is a chemical change?
- two or more substances combined
- entirely new substance
- unable to be reversed
What are the signs of a chemical change?
- fizzes or bubbles
- colour change
- heat given off
- light given off
- odor
- new substance formed
heat required
What is an exothermic reaction?
Gives out excess heat
What is an endothermic reaction?
Uses heat to carry out reaction
