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Natural sciences

Matter, measuring and reactions

Educator section



  • H 2 O
  • Hydrogen and oxygen
  • The elements oxygen and hydrogen joined. This formed a new substance, namely water, that consists of two types of atoms. The atoms joined to form a water molecule.
  • Yes, the elements are combined in a fixed relation to form a new substance with new characteristics.

Assignment 2:


  • 500 oxygen atoms
  • 1 000 oxygen atoms

2. Combination

O 2 Oxygen molecule: two oxygen atoms
NaCl Sodium chloride (table salt): one atom sodium and one atom chloride
N 2 O 5 Sodium oxide molecule: two sodium atoms combine with five oxygen atoms
Fe 2 O 3 Iron oxide: two iron atoms combine with three oxygen atoms
MgCl 2 Magnesium chloride: one magnesium atom combines with two chloride atoms
CO Carbon monoxide: one carbon atom binds to one oxygen atom

Leaner section


Activity: to describe the composition of substances in terms of chemical symbols and formulas [lo 2.3]

When we know the physical and chemical properties of a substance we can use our knowledge to create another substance. Water, a compound, is the best solvent because many substances can dissolve in water. We can use the compound water to obtain gases like hydrogen and oxygen. We can also produce water by mixing these gases.

We make use of chemical symbols to identify elements and use chemical formulas to identify compounds. Here are some chemical symbols:

  • Ag (symbol) is used for silver
  • Fe is used for iron
  • Pb is used for lead
  • Au is used for gold

Try to illustrate the composition of a water molecule:

  • Write the chemical formula for water.


  • Name the two elements that form water?

__________________________________ and _______________________________

  • What had to happen to these elements to form water?

Use the words: elements, atoms and molecules in your explanation.



  • Would this compound depend on a fixed ratio or could it change at random? Motivate your answer.




  • Provide a graphic representation of the atomic composition of water:

Assignment 2

Now try to analyse the chemical formula for carbon dioxide (carbonic acid gas):

Carbon dioxide is a compound of two kinds of atoms. The chemical formula is:


CO 2

This formula signifies that one atom of carbon combines with two atoms of oxygen to form carbon dioxide. We can therefore say that the ratio of carbon atoms to oxygen atoms in carbon dioxide molecules is 1:2.

1. How many atoms of oxygen will have to be present for:

  • 250 carbon atoms?__________________________________________________
  • 500 carbon atoms?__________________________________________________

2. Work out the combinations that are present in the following formulas:

O 2 ____________________________________________________
NaCl ____________________________________________________
N 2 O 5 ____________________________________________________
Fe 2 O 3 ____________________________________________________
MgCl 2 ____________________________________________________
CO ____________________________________________________


Learning Outcome 2: The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

Assessment Standard 2.3: We know this when the learner interprets information by identifying key ideas in text, finding patterns in recorded data, and making inferences from information in various forms (e.g. pictures, diagrams, text).

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Natural sciences grade 7. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11077/1.1
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