Elements, Compounds and Mixtures Flashcards
What is matter?
Anything that has mass and volume, it can be a single chemical substance or a complex mixture of substances
What can matter be separated into?
Mixtures (variable composition) and pure substances (constant composition)
How can pure substances be converted into mixtures?
Physical methods: preparing mixtures
How can mixtures be converted into pure substances?
Physical methods: separating individual components
What can mixtures be separated into?
Heterogeneous and homogeneous mixtures
What is a heterogeneous mixture?
Multiple phase, variable properties within a sample, non-uniform appearance
What is a homogeneous mixture?
Single phase, same properties throughout the mixture, uniform appearance and includes solutions
What is the process called when a gas becomes a solid?
Deposition
Describe the structure of a solid
Regular arrangement, rigid structure, molecules vibrate in space
Describe the structure of a liquid
Assumes the shape of the container, molecules move around one another
Describe the structure of a gas
Assumes volume of container, molecules move rapidly in three dimensions
What is electrical conductivity?
Ability to transmit electricity
What is heat conductivity?
Ability to transfer heat energy
What is density?
Mass-to-volume ration
What is melting point?
Temperature at which a solid becomes a liquid
What is boiling point?
Temperature at which a liquid becomes a gas
What is refractive index?
How light passing through a material is bent
What is malleability?
Ability to be shaped by hammering
What is ductility?
Ability to be shaped by pulling into a wire
What are intensive properties?
Do not depend on the amount of matter present and can be used to identify substances
What are examples of intensive properties?
Density, colour, boiling point
Can intensive or extensive properties be used to identify substances?
Intensive
What are extensive properties?
Depends on the amount of matter present
What are examples of extensive properties
Mass, volume, weight
What are physical properties?
Observed by examining a sample of pure substance and arise from molecular structure and strength of intermolecular interactions
What are chemical properties?
Observed in the course of a chemical reaction and arise from the distribution of electrons around the atom’s nucleus, particularly the outer (valence) electrons
Describe pure substances
- Fixed composition
- Properties do not vary
- Cannot be separated into simpler substances by physical methods
- Can only be changed in identity and appearance by chemical methods
What is an element?
A substance which cannot be split up into two or more simple substances by chemical means
What are compounds?
A substance that contains two or more elements chemically combined in a fixed proportion
What is a molecule?
A group of two or more atoms that are joined together
Describe Atomic Theory
- Observation: elements combine in fixed ratios
- All matter is composed of atoms
- Different elements have different types of atom
- Can be characterised by atomic weight
- All atoms of the same element are identical
- Atoms cannot be made or destroyed
- Compounds are composed of two or more atoms chemically combined in fixed proportions
- Chemical reactions rearrange the atoms, changing the ratios of chemical combination, thus the identity of the compounds
Where is most of the mass of an atom found?
The atom’s nucleus (protons and neutrons)
What is the mass of an electron?
Negligible
What is combining power (valency)?
Ability to form chemical bonds
How is the word Chlorine derived?
Greek for yellowish/green
How is the word Helium derived?
Greek for sun
How is the word Calcium derived?
Latin for lime
How is the word Carbon derived?
Latin for charcoal
How is the word Iron derived?
Anglo-Saxon, symbol Fe is Latin
What is Relative Atomic Mass (RAM)?
The mass of one atom of an element divided by the mass of one twelfth of an atom of Carbon-12
How do you calculate Relative Molecular Mass (RMM)?
Calculated by adding the atomic masses of atoms in a molecule (Mass of one molecule of a substance divided by one twelfth times the mass of one atom of Carbon-12)
Describe mixtures
- Variable composition
- Components retain their identity
- Separable into pure substances by physical methods
- Mixtures of different compositions may have widely different properties
Are colloids homogeneous or heterogeneous?
Visually homogeneous but microscopically heterogeneous
How are mixtures separated?
Uses differences in physical properties
Describe filtration
Select components by particle size (solid/ liquid)
Describe crystallisation
Select components by solubility (solid from solution)
Describe extraction
Select components by solubility (solid or liquid from solution)
Describe evaporation and distillation
Select components by boiling point (from solution or liquid-liquid)
Describe magnetisation
Magnetic metal from other compounds
Describe chromotography
Select components by affinity for solid or mobile phases
