Chemistry - Atoms (AQA)
It was once thought that electrons orbited the nucleus of an atom like planets around a star.

Chemistry - Atoms (AQA)

In order to understand GCSE Science, students must be familiar with the basic and fundamental ideas of Chemistry, such as atoms, bonding and the periodic table of elements. This is the first of six quizzes which will help to clarify these ideas and it looks in particular at atoms.

Atoms are one of the fundamental ideas in Chemistry, but how were they discovered? Greek philosophers were very good at carrying out 'thought experiments'. One of these was done by Democrites who considered what might happen if you took a piece of rock and hit it with a hammer. It's not too difficult to work out that it would shatter. But then he wondered about what would happen if you then took one of the smaller pieces and hit that with a hammer and so on. He decided that you would probably end up with a piece so small that it could not be broken any smaller. The Greek word for 'indivisible' was 'atomos' and that is the origin of the word 'atom'.

Almost 2000 years later, the idea of atoms re-surfaced. They were seen in the same way as Democritus saw them - small, solid spheres. That seemed very logical but gradually, scientists began to discover that the 'indivisible' atoms were in fact divisible which led to the idea that atoms were more like a current bun - a lump of matter with the particles spread through it. Later, it was found that atoms were mainly open space with a tiny nucleus and the electrons were regarded as orbiting like planets. Then in the 20th century it was realised that electrons orbit the nucleus in 'shells' and the discovery of neutrons completed the picture.

It was realised also that the number of electrons in the outer shell determined the chemical properties of a particular atom. In fact, the arrangement of electrons is the basis for another fundamental part of Chemistry - the periodic table... but that's a whole different story for another quiz!

An element is made up from what?
Two or more different types of atom
One type of atom
An easy start - or was it? If you don't know your definitions of elements and compounds, revise them hard before the exam arrives
Which of the following elements is not found in CaHCO3?
Atoms are represented by symbols. Where the symbol has more than one letter, only the first one is a capital. That's what makes this question tricky. A lot of students see the CO part of the formula and immediately think it is cobalt. It is not as there are 2 capital letters. So the moral of this is to pay attention to the capital letters!
What particles are present in the nucleus of an atom?
Protons only
Neutrons only
Electrons only
Protons and neutrons
Ernest Rutherford was the famous scientist who lead the team that discovered the nucleus
Where are the electrons found?
In a single group close to the nucleus
Orbiting the nucleus like the planets of the Solar System
In 'shells' surrounding the nucleus
Fixed in place at different distances from the nucleus
The shells are not physical things, they are just the areas where you will find the electrons as they orbit the nucleus. They can also be referred to as energy levels
Which of the following give the charges in order for the proton, neutron and electron?
+1, 0, -1
0, +1, -1
-1, +1, +1
+1, +1, -1
If you weren't sure, you can remember the charges like this:
Protons - P for positive
Neutrons - NEUT for neutral
So the electrons must be negative
Which of the following statements is true in an atom?
The number of protons is always equal to the number of electrons
The number of protons is always equal to the number of neutrons
The number of protons is sometimes equal to the number of electrons
The number of protons is never equal to the number of electrons
The important thing to remember about atoms is that they are electrically neutral so the positive charges of the protons are balanced by having the same number of electrons. If they are not the same, you have an ion, not an atom
Atoms of a particular element all have the same number of what?
The number of protons is what gives each element its own unique identity. So all atoms that contain 6 protons in the nucleus will be the element carbon, regardless of the number of neutrons
The element Argon has an atomic number of 18 and a mass number of 40. Which of the following statements is true.
Argon has 18 protons and 22 neutrons
Argon has 18 neutrons and therefore 18 electrons
Argon has 18 electrons and 22 protons
Argon has 18 neutrons and 22 protons
The atomic number gives you the number of protons (and therefore the number of electrons) in the atom. It is sometimes called the proton number.The mass number is the total number protons plus neutrons. If you subtract the atomic number from the mass number you get the number of neutrons
Which of the following represents the arrangement of the 18 electrons in the Argon atom?
The first 3 electron shells (energy levels) are all complete which is what makes it so difficult to get argon to react with anything
The element sodium has an atomic number 11 and mass number 23. Which of the following gives the correct number of protons, neutrons and the electron arrangement in the correct order?
23, 11, (2.8.1)
12, 11, (2.6.3)
11, 12, (2.8.1)
11,12, (8.2.1)
Sodium is in group I of the periodic table because it has 1 electron in its outer energy level
You can find more about this topic by visiting BBC Bitesize - Atoms, elements and compounds - AQA

Author:  Kev Woodward

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