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Periodic table of elements
chapter 8 chemistry
Terms in this set (67)
what did john dalton do?
he compared the weight of other elements to that of hydrogen
what did johann Dobreiner do?
divided the elements in to groups based on their atomic weights
What did John Newlands do?
arranged the elements by atomic weight and started to notice patterns.
Who was Dimitri Mendeleev and what did he do?
- Russian scientist
- arranged the elements based on atomic mass and how many other atoms they could make bonds with
- left gaps in the table for elements he predicted would be discovered.
what is the atomic mass number?
protons + neutrons
what is the atomic number?
number of protons (equal to electrons)
How is the periodic table organized?
organised into groups (vertical) and periods (horizontal)
what do the periods tell us?
number of electron shells
what do the groups tell us?
number of electrons on the outermost electron shell
- arranged in shells around the nucleus
- 1st electron shell: max 2 electrons
- 2nd electron shell: max 8
- stable atoms have a full outermost cell
- written as the number of electrons in each cell (eg. C is 2,4)
Why do electrons share electrons
- atoms want to be stable
- they are most stable when they have a full outermost shell
- 2 atoms can share a pair of electrons to achieve this
what is a covalent bond?
A shared pair of electrons
what are the group 1 metals?
(they themselves are not alkalis but the oxides and hydroxides they form are)
properties of group 1
- conduct electricity
- shiny when freshly cut
- soft (can be cut easily)
- low melting points
- low density
- exciting reactions with water; zoom around surface of water, make hydrogen gas and an alkaline solution
why do group elements have similar properties?
they have similar electron arrangements, which depends on the number of electrons in outermost shell
group 1 organisation
boiling points decrease from top to bottom of group
Alkali metals and uses
lithium - batteries
sodium - street lamps for orange glow, (ions) needed by the body to conduct nervous impulses.
potassium- (nitrate) fertilizer;
what are the group 2 metals?
alkaline earth metals
what are the physical properties of group 2 metals?
- low densities and melting points
as u move down group 2:
- density decreases
- melting point decreases
- boiling point decreases
what are the chemical properties of group 2 metals?
metals arent alkalis, oxides and hydroxides dissolve slightly in water to make alkaline solutions
- react w oxygen in the air
- reactivity increases as u move down group 2
- all burn in pure oxygen to produce oxides
group 2 metals and uses
beryllium: combines with aluminium, silicon, o to make beryl (emeralds)
magnesium: brilliant white lights in firework
calcium: forms compunds used in baking powders, medicines and plastics, form healthy teeth and bones
what are group 7 elements called?
Halogens (greek word for salt former, elements in this group form salts readily)
physical properties of the halogens
as you move down:
- melting point increases
- boiling point increases
chemical properties of the halogens
- fluorine is the most reactive ( can form compounds with noble gases)
- fluorine reacts with water vigorously to produce oxygen and hydrogen fluoride
- chlorine dissolves in water -> hydrochloric acid
- bromine dissolves in water but reacts slowly
- iodine does not react with water
uses of halogen elements
- fluorine: prevents tooth decay and is added to some drinking water supplies
- chlorine: kills bacteria in water supply systems
- bromine: light sensitive, used in photographic film
what are the group 0/8 gases called?
the noble gasses (very unreactive)
uses of noble gases?
- helium: used to lift meteorlogical balloons into atmosphere
- neon: used in lights
- argon: in wire filament light bulbs
- krypton: used in lamps of high intensity
- xenon: makes bright light
characteristics of hydrogen
- has no neutrons, only a proton and electron
- lightest element
- colourless gas
- most common element in the universe
hydrogen as fuel
- highly explosive when it reacts with oxygen
- when compressed, it is carefully released into the engine and combusted to produce only water vapour.
- no carbon dioxide is produced
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