# 5.4 Writing formulae

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## The formulae of covalent compounds

To work out the formulae of covalent compounds, we need to use the valency of the atoms in the compound. This is because the valency tells us how many bonds each atom can form. This in turn can help to work out how many atoms of each element are in the compound, and therefore what its formula is. The following are some examples where this information is used to write the chemical formula of a compound.

Write the chemical formula for water

1. A molecule of water contains the elements hydrogen and oxygen .

2. The valency of hydrogen is 1 and the valency of oxygen is 2. This means that oxygen can form two bonds with other elements and each of the hydrogen atoms can form one.

3. Using the valencies of hydrogen and oxygen, we know that in a single water molecule, two hydrogen atoms will combine with one oxygen atom. The chemical formula for water is therefore:

$\mathrm{H}{}_{2}\mathrm{O}$ .

Write the chemical formula for magnesium oxide

1. A molecule of magnesium oxide contains the elements magnesium and oxygen .

2. The valency of magnesium is 2, while the valency of oxygen is also 2. In a molecule of magnesium oxide, one atom of magnesium will combine with one atomof oxygen.

3. The chemical formula for magnesium oxide is therefore:

$\mathrm{MgO}$

Write the chemical formula for copper (II) chloride.

1. A molecule of copper (II) chloride contains the elements copper and chlorine .

2. The valency of copper is 2, while the valency of chlorine is 1. In a molecule of copper (II) chloride, two atoms of chlorine will combine with one atom of copper.

3. The chemical formula for copper (II) chloride is therefore:

$\mathrm{CuCl}{}_{2}$

## The formulae of ionic compounds

The overall charge of an ionic compound will always be zero and so the negative and positive charge must be the same size. We can use this information to work out what the chemical formula of an ionic compound is if we know the charge on the individual ions. In the case of $\mathrm{NaCl}$ for example, the charge on the sodium is $+1$ and the charge on the chlorine is $-1$ . The charges balance ( $+1-1=0$ ) and therefore the ionic compound is neutral. In $\mathrm{MgO}$ , magnesium has a charge of $+2$ and oxygen has a charge of $-2$ . Again, the charges balance and the compound is neutral. Positive ions are called cations and negative ions are called anions .

Some ions are made up of groups of atoms, and these are called compound ions . It is a good idea to learn the compound ions that are shown in [link]

 Name of compound ion formula Name of compound ion formula Carbonate $\mathrm{CO}{}_{3}^{2-}$ Nitrite ${\mathrm{NO}}_{2}^{-}$ Sulphate ${\mathrm{SO}}_{4}^{2-}$ Hydrogen sulphite ${\mathrm{HSO}}_{3}^{-}$ Hydroxide ${\mathrm{OH}}^{-}$ Hydrogen sulphate ${\mathrm{HSO}}_{4}^{-}$ Ammonium ${\mathrm{NH}}_{4}^{+}$ Dihydrogen phosphate ${\mathrm{H}}_{2}{\mathrm{PO}}_{4}^{-}$ Nitrate ${\mathrm{NO}}_{3}^{-}$ Hypochlorite ${\mathrm{ClO}}^{-}$ Hydrogen carbonate ${\mathrm{HCO}}_{3}^{-}$ Acetate (ethanoate) ${\mathrm{CH}}_{3}{\mathrm{COO}}^{-}$ Phosphate ${\mathrm{PO}}_{4}^{3-}$ Oxalate ${\mathrm{C}}_{2}{\mathrm{O}}_{4}^{2-}$ Chlorate ${\mathrm{ClO}}_{3}^{-}$ Oxide ${\mathrm{O}}^{2-}$ Cyanide ${\mathrm{CN}}^{-}$ Peroxide ${\mathrm{O}}_{2}^{2-}$ Chromate ${\mathrm{CrO}}_{4}^{2-}$ Sulphide ${\mathrm{S}}^{2-}$ Permanganate ${\mathrm{MnO}}_{4}^{-}$ Sulphite ${\mathrm{SO}}_{3}^{2-}$ Thiosulphate ${\mathrm{S}}_{2}{\mathrm{O}}_{3}^{2-}$ Manganate ${\mathrm{MnO}}_{4}^{2-}$ Phosphide ${\mathrm{P}}^{3-}$ Hydrogen phosphate ${\mathrm{HPO}}_{4}^{3-}$

how environment affect demand and supply of commodity ?
Wht at the criteria for market ?
Amos
what is difference between monitory policy and fiscal policy?
monetary policy is a policy thrust by National Govt(CBN) to influence government spending, purchase &taxes
Frank
necessity of economics
I will say want,choice,opportunity cost,scarcity,scale of preference
Alao
what is monopoly market.How price output are determined under monopoly market
bisham
b) Monopoly market is an impecfect market where s single firm having the innovation to produce a particular commodity.Prices are determined through output since there are no other competitive.
Frank
Monopoly market:firm has market power & does not respond to market price
Frank
Explain the process of price determination under perfect competition market with suitable diagram
Price determination under perfect competition via this process :firms have no market power to influence price rather firms respond to market price.
Frank
price is different from demand- demand is amount of commodity
demand is amount /quantity of commodity a potential buyer is willing to buy at a given price at market
Frank
demand is a desire of customer on commodity with the ability to pay it and willing to buy it at given price of commodity
Harika
demand is price of what
show that shortrun average cost
what is economics
what is money
Mbah
what is money
Mbah
Difine macro economics
agaba
money is a medium of exchange between goods and services,maybe inform of currency.
Wesonga
Economics is study of how human beings strive to satisfy numerous wants using limited available resources.
Wesonga
how do you find the maximum number of workers the firms should employ order to produce where there are increasing returns
Jane
what are implications of computing national income?.
agaba
pl
MUDASIRU
what is the formulae for calculating national income
MUDASIRU
it calculated by value added method
Praveen
classify the production units like agriculture, banking, transport etc
Praveen
money is anything that is generally acceptetable for human
Ogbaji
Estimate the net value added(NVA) at fixed cost by each industrial structure
Praveen
definition of unemployment
what are the causes of unemployment?
The main causes of unemployment are listed below. 1. Frictional unemployment 2. Cyclical unemployment 3. Structural unemployment
assani
We can also categorize the causes on a broader sense as: 1. Political and 2. Social cause As unemployeement root causes are embaded in this two.
Yonathan
would opportunity cost exist if there was no scarcity?
assani
yes just because the opportunity cost arose when there is Alternative to choose among the alternatives.
I am thinking that, if our resources were unlimited, then there wouldn't be any need to forgo some wants. Hence the inexistence if opportunity cost
assani
Politics
Job
politics has done what?
assani
consider time assani
Mary
I'm Emmanuel,...I taught the main cause is the change in gov't.
Emmanuel
...Lack of capital to set up a firm respectively
Emmanuel
🙈
Emmanuel
I would like to bring in Educational levels can also be the cause the cause of the problem respectively
Emmanuel
I think the main causes of unemployment is lack of INFRASTRUCTURAL DEVELOPMENT OVER POPULATION OVER DEPENDENT ON GOVERNMENT LACK OF SELF EMPOWERMENT...
ananti
lack of skills among the new generation is the serious issue.
Vishal
Where I come from , I don't see why education or personal aspects seem to do with unimployment, technically the motivation and eigerness in all works of live is there , dispite the cultural influence and physical bearriors;the thing we lacking is Government Support and open market ethics.
Joe
sorry about that-(repation). We have a over powering ethical political system that's displacing the marketing asspects of economy and causing large scale unemployment right across the board...
Joe
can someone Explain Expansionary Monetary Policy and Contractionary Monetary Policy Using one of the instrument of Monetary Policy? Please am kinda lost here?. ta
using a graph show the case of substitute and compliment goods
can anyone give me a simple explanation to Five Sector Macroeconomics?
Emmanuel
Can someone please define what economics is
economics simply is a social science subject that study human behavior.
dajan
economics is a social science which studies human behaviour as a relationship between ends and scarce means that has alternative uses
Alao
Can someone please tell me how to calculate GDP
Emmanuel
emmanual kapal to calculate GDP (Gross Domestic Product) has three method in calculating it (1)income approach (2) expenditure approach (3) value added method
Alao
thanks Alae
Emmanuel
u are welcome
Alao
in basic terms economics is revered to as battery system, it date back to when Men sees the need to exchange sapless goods and produce to gain , either wealth , basic necessities or to establish trading ties for personal benefit or social asspects in terms of coexistence and continuity, future .
Joe
what is the law of demand
keep other thing constant, when the price increases demand decrease when the price decreases demand increases of the commodity.
sj
all things being equal,quantity demanded decrease as price increase and increase as price decrease
Seth
there's practial joke to it ..." the higher the demand ; scarcity, increase in production and drop in quality"... quite the controversy - for example China vs Europe, United States and we are all boxed up in between somewhere...
Joe
Other thing remain constant the low price of commodity the high quantity of commodity and vice versa is true
Baraka
Explain Effective demand
What is effective demand
Anita
like Modi is in demand...best example of effective demand
Pranav
Don't get you
Anita
Anita you mean you don't get me or who?
Onyeking
level of demand that represents a real intention to purchase by people with the means to pay
Pranav
Difference between extinct and extici spicies
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
The fundamental frequency of a sonometer wire streached by a load of relative density 's'are n¹ and n² when the load is in air and completly immersed in water respectively then the lation n²/na is
Properties of longitudinal waves