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C1- atomic structure and the periodic table - Coggle Diagram
C1- atomic structure and the periodic table
chemical symbols
all substanes are made of tiny particles called atoms and is the smallest part of an element that can exist
atoms of each element are represneted by their own chemical symbol which consists of:
one or two letters
always start with a capital letter, with any other lower case letter
for example -
O is oxygen atom
Na is sodium atom
Fe is iron atom
K is potassium atom
elements in red are metals and yellow are non metals
chemical formulae of elements
a chemical formula is used to represent an element or compound in balanced chemical equations
the formula for most elements is just its chemical symbol eg:
helium, He
lithium, Li
beryllium, Be
boron, B
carbon, C
neon, Ne
magnesium, Mg
some non metals exist as molecules that are made up of two atoms joined together where the number is subscripted eg:
iodine, I2
bromine, Br2
chlorine, Cl2
flourine, F2
oxygen, O2
nitrogen, N2
hydrogen, H2
chemical formulae for elements
a compound is a substance that contains two or more elements that are chemically combined
the elements in a compound are present in fixed proportion
eg. carbon dioxide always has 12 g of carbon for every 32 g of oxygen
a chemical formula can be used to represent a compound
the formula shows:
the symbols for each element in the compound
the number of atoms of each element in a unit of the compound
for example, magnesium oxide is made up of two elements, magnesium and oxygen with the formula MgO which shows that there is one magnesium atom and one oxygen atom
some examples of compounds and their formulae
the subscript number in a formula shows if there is more than one atom of an element:
sodium chloride - NaCl
potassium bromide - KBr
magnesium iodide - MgI2
carbon dioxide - CO2
carbon monoxide - CO
sulfar trioxide - SO3
water - H2O
ammonia - NH3
methane - CH4
many compounds exists naturally but they can alo be formed from their elements in chemical reactions
in a chemical reaction, one or more new substances are formed
most chemical reactions involve energy changes
chemical formulae of ions
an ion is a charged particle formed when an atom, or groups of atoms, loses or gains electrons
the number an sign of its electrical charges are shown in a superscript text
names and formulae of some common atoms:
sodium, Na^+ - one posative
magnesium, Mg^2+ - two posative
chloride, Cl^- - one negative
oxide, O^2- - two negative
simple formulae
the formula for an ionic compound can be pridicted using the formulae of its ions
the number of ions in a formula must give an equal number of positive and negative charges
sodium chloride, NaCl - one positive, one negative
sodium oxide, Na2O - two positive, two negative
magnesium oxide, MgO - two positive, two negative
magnesium chloride, MgCl2 - two positive, two negative
word equations
a word equation represents a chemical reaction using the names of the substances involved and do not show any chemical symbols or formulae
reactants and products -
reactants are substances that react in a chemical reaction
in a chemical reaction, the atoms or ions in reactants seperate from one another
they join back together in differnt ways to for products
word equations always take the form -
reactants --> products
a + sign seperates two or more reactants, or two or more products
example word equations -
potassium hydroxide reacts with sulfuric acid
potassium sulfate and water are formed in the reaction
this means that:
the reactants are postassium hydroxide and sulfuric acid
the products are potassium sulfate and water
the word equation - potassium hydroxide + sulfuric acid --> potassium sulafte + water
there can be different numbers of reactants and products eg:
sodium + chlorine --> sodium chloride
calcium carbonate --> calcium oxide + carbon dioxide
balanced chemical equations
a balanced chemical equation represents a chemicla reaction using the formulae of the reactants and the products
it shows the number of units of each substance involved
state symbols -
balanced chemical equations sometimes include state symbols in brackets after each formula and they show the physical state of that substance
(s) - solid
(l) - liquid
(g) - gas
(aq) - aqueous solution
an aqueous solution is formed when a substances is dissolved in water
state symobols are useful because they show what a substance is like eg:
H2O(l) is liquid water but H2O(g) is steam and H2O(s) is ice
HCl(g) is hydrogen chloride gas but HCl(aq) is hydrochloric acid
balancing an equation -
the law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the total mass of the products is equal to the total mass of the reactants
this means that chemical reactions can be represented by symbol equations
a balanced symbol equation has the same number of atoms of each element on both sides of the arrow
to balance an equation, add numbers to the left of one or more formulae
here s one way to work out how to do this for the reaction between nitrogen and hydrogen:
check to see if there are an equal number of atoms of each element on both sides, they are not - N2 + H2 → NH3
there are two nitrogen atoms on the left but only one on the right, so put a big 2 on the left of the NH3 - N2 + H2 → 2NH3
check again, there are two hydrogen atoms on the left but (2 × 3) = 6 on the right, so put a big 3 in front of the H2 - N2 + 3H2 → 2NH3
check again to see if there are equal numbers of each element on both sides, they are - (two nitrogen atoms and six hydrogen atoms)
add the state symbols if asked to do so - N2(g) + 3H2(g) → 2NH3(g)
