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OCR 21stC science C4

OCR 21st Century Science C4

Relative atomic mass is the comparison of an atom's mass to []'s (the []est) hydrogen's--lightest--.
In a periodic table, a [] of elements is a vertical column group--.
The elements in a group in the periodic table have similar properties. For example, group 1 contains sodium and other very reactive []s while group 7 contains lithium and other very reactive []-[]s metals-- non-metals--.
A row of element in the periodic table is called a period.
Chemical symbol for lithium: Li
Chemical symbol for sodium: Na.
Chemical symbol for potassium: K.
When alkali metals are freshly cut they are shiny, but they tarnish rapidly in []t []r due to reaction with [] moist air--oxygen--.
Lithium, sodium and potassium all react vigorously with [] and [] air and water.
Alkali metals react with water to form [] gas and an [] solution of a [] hydrogen--alkaline--hydroxide--; the formula is given as H+M[] where M represents a group [] metal OH--1--.
The group 1 metals are refered to as alkali metals
A[] []s vigorously react with chlorine to form []less, []ine s[]s with the formula [] Alkali metals--colourless, crystalline salts--MCl--.
The shiny surface of sodium tarnishes []er than that of lithium, while sodium tarnishes [] than potassium; quicker--slower; this shows the increasing []ty of the metals as we go down the group reactivity--.
Because, the alkali metals are so []e, care has to be taken when using them reactive--. They must not be t[]ed as they will react with [] in [] on the [] touched--water--sweat--skin--. G[]es may be used and g[]s should be worn gloves--goggles--.
The group 7 elements are also known as the halogens.
Chemical symbol of chlorine: Cl.
Chemical symbol of bromine: Br.
Chemical symbol of iodine: I.
The halogens consist of []c molecules diatomic--.
As you go down the group, halogens become [] reactive less. Flourine, at the top of the group, is the most reactive halogen. It is very dangerous and can cause severe chemical b[]s on contact with skin. burns--.
The relative reactivity of halogens can be shown by looking at [] reactions displacement--.
|Displacement Reactions| When chorine (gas or dissolved in water) is added to sodium bromide solution, the [] takes the place of the [] because its more [] and displaces [] from the [] []. chlorine--bromine--reactive--bromine--sodium bromide--. The solution turns brown, the brown colour being the []d []. The chlorine has gone to form [] [] displace bromine--sodium chloride--. chlorine + sodium bromide --> sodium chloride + bromine.
Halogens are very []e and p[], hence care must be taken reactive--poisonous--. Chlorine is used only in a []e []d, iodine should not be handled as it wil damage the []; g[]s may be used, and g[]s should be worn fume cupboard--skin--gloves--goggles--.
The state symbol (s) means solid.
The state symbol (l) means liquid.
The state symbol (g) means gas.
The state symbol (aq) means aqueous (dissolved in water).
An atom is a composition of protons and neutrons in a very small central [] and electrons arranged in []s around the nucleus nucleus--shells--.
Protons and neutrons have the same m[], which is about [] times larger than an electron's. mass--2000--. An electron's mass is generally taken as 0 for being neglible.
The elements in the periodic table are arranged according to the their [] number atomic--.
All the atoms of the same element have the same number of p[] protons. The number of protons will be equal to the number of []s electrons--.
Some elements emit distinctive []e colours when []ed flame--heated--, e.g. l[]um, s[]um and p[]um lithium, sodium and potassium.
The light emitted from a particular element gives a characteristic [] s[] line spectrum.
Scientists have used line spectra to discover new e[]ts. In fact the discovery of some elements, such as the r[]dium and c[]ium, owuld not have been possible if not of spectroscopy elements--rubidium--caesium--. The element helium was discovered by studying line spectra emitted by the [] Sun.
The discovery of some elements depended on the development of new []cal t[]s practical techniques-- e.g. s[]opy spectroscopy--.
Electrons are contained in s[]s around the []s, also called []y l[]s shells--nucleus--energy levels. A shell (or [] level) fills with electrons across a [] energy--period-- (thus elements in the same group have the same number of electrons in their outer shell, this number being the group number).
Elements in the same [] have the same number of electrons in their outer shell and this number is the [] number group--group--.
When lithium is added to water it []s, f[]ing steadily and becomes []er until it eventually d[]rs floats--fizzing--smaller--dissappears--.
Protons has a relative mass of [] unit(s), while neutrons have one of [] unit(s) 1--1--. The relative atomic mass is thus the number of [] + number of [] protons--neutrons--.
The relative atomic mass - number of protons = number of neutrons. Atomic number = number of []s = number of []s protons--electrons--.
Molten (i.e. melted) compounds of metals with non-metals c[] electricity, which is eevidence that they are mde up of []ed particles called []s conduct--charged--ions--.
An ion is an [] (or group of []s) which has gained or lost []s and thus has an overall []e atom--atoms--electrons--charge.
The alkali metals (group 1) form ionic compounds when they react with []-[]s; their ions have a []ive charge of [] non-metals --positive--1--. For example, sodium forms sodium ions, Na^[] (M^n+ has n electrons [] than an a[] its type) +--less--atom--.
The halogens (group 7) form ionic compounds when they react with []s; their ions have a []ive charge of [] metals --negative--1--. For example, chlorine forms chlorine ions, Cl^[] (M^n- has n electrons [] than an a[] its type) - --more--atom--.
If one knows the charges on the ions in an []ic c[]d, one can work out its formula ionic--compound--. To do so, simply balance b[]e the positive and negative []es: e.g. calcium has ion Ca^2+ while chlorine has ion Cl^-, meaning the formula is [] balance--charges--CaCl2[ss]--.
If one has the formula of an []ic c[]d and the charge of one of the two ions, one can work out the charge of the other ion ionic--compound--. To do so, simply look at what b[]es the c[]es: eg. take Na2O, knowing a sodium ion is Na^+ - the oxygen ion must be [] balaces--charges-- O^2- --.
As group 7 elements are non-metals, the compounds of halogens with alkali metals are []ic ionic--.
Solid ionic compounds form c[]s because ions are arrange in a r[]r l[]e crystals--regular--lattice--.
[] ionic compounds do not conduct electricity as the ions are held firmly in []ce; they cannot [] to conduct the electric current solid--place--move--.
When an ionic compound melts, the charged ions are free to [] independently in the liquid, meaning that []en ions do [] electricity move--molten--conduct--.
When a crystal of an ionic compound dissolves, the ions s[]e, meaning that the ions are free to [] inependently in the liquid, so a solution of an ionic compound in water []s electricity separate-moves--conducts--.
=Line spectra= All atoms give off []t when heated, although sometimes this light is not visible to the human eye. light--.A p[]sm is used to s[]t the light to form a s[], and each element has a distinctive l[] s[] [#b4#]
The innermost (first) shell can hold up to [] electron while the second shell can hold up to [] 2--8--; for the first 20 elements, the third shell can hold up to [] 8--.
An electron configuration of 2 electrons then 8 then 8 would be shown as: 2[]8[]8 2.8.8 -- or through dots in circles. [#C6#]
At room temperature and pressure, chlorine's state is [] and is y[]-[] in colour gas--yellow-green--. At room temperature and pressure, bromine's state is [] and it's []-b[] in colour liquid--red-brown--. At room temperature and pressure, iodine's state is as a [] and it's colour is a d[] []e solid--dark--purple--.
At room temperature and pressure, Bromine, unlike gas chlorine, is a liquid -- coloured red-brown. When it's a gas, it's []wish-b[] in colour yellowish-brown--.
At room temperature and pressure, iodine is a dark purple solid, while as a gas it is [] []e dark purple--.
Group 1 elements are also known as [] me[]s alkali metals.
Lithium, Sodium, Potassium, Rubidium and Caesium are all in group [] of the Periodic table 1.
All the alkali metals react v[]ly with cold water. In each reaction [] gas is given off and the metal []de is produced vigorously--hydrogen--hydroxide--. The state of the alkali metals is obviously [] while the metal hydroxide's are a[] al[]ne []tions solid--aqueous--alkaline--solutions--.
All the alkali metals react vigorously with cold water. The s[] and vi[] of the reaction increases as you go 1 the group speed--violence--. This shows the []ty of the alkali metals increases as you go down Group 1 reactivity--.
When Sodium is added to water, the sodium []s to form a [] that moves around on the s[] melts--ball--surface--. It []es []ly, and the hydrogen produced may b[] with an []e []e before the sodium d[]s fizzes rapidly--burn--orange flame--disappears--.
When potassium is added to water, the metals []s and []s--it moves around []ly on the []e of the water--the hydrogen []es []tly melts--floats--quickly--surface--ignites instantly--. The metal is also set on []e, with s[]s and a l[] flame; there is sometimes a small e[] at the end of the reaction fire--sparks--lilac--explosion--.
lithiu + water → lithium hydroxide + hydrogen, or as a chemical equation: 2Li(s) + 2H₂O(l) → 2LiOH(aq) + H₂(g)
sodium + water → sodium hydroxide + hydrogen, or as a chemical equation: 2Na(s) + 2H₂O(l)→ 2NaOH(aq) + H₂(g)
potassium + water → potassium hydroxide + hydrogen, or as a chemical equation: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g).
The trend in reactivity for halogens (decreasing as you descend) can be shown in []ment reactions where the [] reactive element displaces the [] reactive one displacement--more--less--, and is evident in their reactions with [] m[]s and with i[] alkali metals--iron--.
Because the halogens are very []e and []us, care must be taken when using them reactive--poisonous--. Chlorine is used only in a f[] c[]. Iodine should not be h[]ed (it will damage the []n) fume cupboard--handled--skin--. G[]s may be used and g[]s must be worn gloves--goggles--.
The chemical formua for Hydrogen: H₂.
The chemical formula for chloride is [] as it's an []n C⁻ as it's an anion-- (though it may not always be shown as such, e.g. 2NaCl). The chemical formula for bromide is [] while the chemical formula for iodide is [] anion-- Br⁻ -- I⁻ --. Chlorides, bromides and iodides made up the group known as the halides.
Atoms of each element have a different [] number (i.e. number of []s), proton--protons--; also called [] number atomic--.
Arranging the elements according to their atomic number gives []g patterns in the []s of elements repeating--properties--; each element in the periodic table is placed in a [] with those of similar properties column
Created by: Toluo



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