Atomic Structure and the Periodic Table Flashcards
What is an atom?
smallest part of an element that can exist
What is an element?
a substance made of only one type of atom
Where are elements listed and approximately how many are there?
- listed in periodic table
- approximately 100
Elements can be classified into 2 groups based on their properties; what are these groups?
metals and non-metals
Elements may combine through chemical reactions to form new products; what are these new substances called?
compounds
What is a compound?
2 or more elements combined chemically in fixed proportions which can be represented by formulae
Do compounds have the same properties as their constituent elements?
no
What is a mixture?
2 or more elements or compounds not chemically combined together
Do mixtures have the same properties as their constituent elements?
yes
What are 5 methods through which mixtures can be separated? Do they involve chemical reactions?
- filtration
- crystallisation
- simple distillation
- fractional distillation
- chromatography
they do not involve chemical reactions
Describe and explain simple distillation
- used to seperate liquid from a solution
- liquid boils off and condenses in the condenser
- thermometer will read the boiling point of the pure liquid
- contrary to evaporation, we get to keep the liquid
Describe and explain crystallisation/evaporation
- evaporation separates a solid dissolved in a solvent from a solvent
- solution heated until all solvent evaporates, solid stays in vessel
- crystallisation is similar, but only some of the solvent is removed by evaporation to form a saturated solution
- the solid starts to crystallise as it becomes less soluble at lower temperatures
- crystals can be collected and separated from the solvent via filtration
Describe and explain fractional distillation
- separating a mixture of liquids where the liquids have different boiling points
- apparatus similar to simple distillation, with an additional fractionating column on top of the heated flask - fractionating column contains glass beads to help separate the compounds
- in industry, mixtures are repeatedly condensed and vapourised
- column is hot at bottom and cold at top
- liquids condense at different heights of the column
Describe and explain filtration
- used to separate insoluble solid suspended in a liquid
- residue gets caught in filter paper (particles too big to fit through holes in paper)
- filtrate is the substance that comes through the filter paper
- apparatus: filter paper & funnel
Describe and explain chromatography
- separate mixture of substances dissolved in a solvent
- paper chromatography: paper with a spot containing a mixture in a beaker with some solvent, bottom of paper must be in contact with the solvent, solvent level will start to rise, thus separating the spot (mixture) into few spots (components)
What is a separating funnel?
- apparatus for separating immiscible liquids
- 2 immiscible liquids of different densities will form 2 distinct layers in the separatory funnel
- we can run off the bottom layer (liquid with greater density) to a separate vessel
Describe the plum-pudding model
the atom is a ball of positive charge with negative electron embedded in it
Describe the Bohr/nuclear model & how it came about
the nuclear model suggests that electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiments
Later experiments led to the discovery of smaller, positive particles in the nucleus; what are these particles called?
protons
What did the work of James Chadwick provide evidence for?
the existence of neutrons in the nucleus
Describe the structure of an atom
the atom has a small central nucleus (made up of protons and neutrons) around which there are electrons
State the relative masses and relative charges of the proton, neutron and electron
masses - 1, 1, very small
charges - 1, 0, -1
Explain why atoms are electrically neutral
they have the same number of electrons and protons
What is the radius of an atom?
0.1 nm
What is the radius of a nucleus and what is it compared to that of an atom?
1 x 10^-14m and 1/10000
What name is given to the number of protons in the nucleus?
atomic number
Atoms of the same element have the same number of which particle in the nucleus?
protons
Where is the majority of mass of an atom?
nucleus
What is the mass number?
the total number of protons and neutrons
How does one calculate the number of neutrons using mass number and atomic number?
subtract the atomic number from the mass number
What is an isotope?
atoms of the same element (same proton number) that have a different number of neutrons
Do isotopes of a certain element have the same chemical properties?
they have the same chemical properties because they have the same electronic structure
What is the relative atomic mass?
the average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where the mass of C(12) is 12