Atomic Structure Flashcards
What is an element?
A substance made of only one type of atom.
What is a compound?
A substance formed from two or more elements chemically bonded in fixed proportions.
What is a mixture?
Two or more substances (elements or compounds) that are not chemically bonded together.
Give 4 physical separation techniques used for mixtures.
Filtration, crystallisation, simple distillation, fractional distillation.
What is filtration used for?
To separate an insoluble solid from a liquid.
What is crystallisation used for?
To obtain pure crystals of a soluble solid from a solution by evaporating the solvent.
Describe how to carry out crystallisation.
- Gently heat the solution to evaporate some of the solvent.
- Leave it to cool so crystals form.
- Filter the crystals and dry them.
What is simple distillation used for?
To separate a solvent from a solution (e.g., water from salt water).
How does simple distillation work?
• Heat the solution until the solvent evaporates.
• The solvent is then cooled in a condenser and collected.
What is fractional distillation used for?
To separate a mixture of liquids with different boiling points.
Describe how fractional distillation works.
• Heat the mixture.
• The liquid with the lowest boiling point evaporates first.
• It is condensed and collected.
• Higher boiling point substances follow.
What is chromatography used for?
To separate and identify substances in a mixture (often coloured dyes or inks).
What is the stationary and mobile phase in chromatography?
• Stationary phase: the paper
• Mobile phase: the solvent (e.g. water or ethanol)
What do substances that travel further in chromatography have in common?
They are more soluble in the solvent and less attracted to the paper.
How do you calculate Rf value in chromatography?
Rf = distance moved by substance ÷ distance moved by solvent.
Why was Mendeleev’s periodic table better than earlier ones?
• He left gaps for undiscovered elements.
• He grouped elements by properties, not just atomic mass.
How did Mendeleev predict undiscovered elements?
He used patterns in group properties to estimate their masses and chemical behaviour.
Why was the modern periodic table accepted later?
The discovery of protons and atomic number explained why elements fit better when ordered by atomic number, not mass.
What do periods in the periodic table represent?
The number of electron shells in the atoms.
What do groups in the periodic table represent?
The number of electrons in the outer shell.
Why do Group 1 elements react in similar ways?
They all have 1 electron in their outer shell.
Why is the noble gas group (Group 0) unreactive?
Their atoms have full outer shells, so they are stable and do not need to gain or lose electrons.
Properties of transition metals
-Form coloured compounds -Hard and strong -Less reactive -Higher Density -High melting points -Used as catalysts
