Q1. What is an element?
Ans. It is a substance that cannot be split into other substances.
Water is not an element because it can be split into the gases oxygen and hydrogen. Oxygen and hydrogen are elements because they cannot be split. Every element has its own atomic number. This is the number of protons in its nucleus, which is balanced by the same number of electrons.
Q4. What is the smallest particle of all?
Ans. No one is sure. Atoms are made of protons, neutrons and electrons. In turn, these could be made of even tinier particles-quarks and leptons. But one day, we might discover even smaller particles.
Q10. How many kinds of particle are there?
Ans. Since the 1920s, scientists have discovered that there are at least 200 kinds of sub-atomic particle besides electrons, protons and neutrons. Most of these are created in special conditions and exist only for a fraction at a time.
Q9. Who split the atom?
Ans. Electrons can be split off from atoms easily, but in 1919, the New Zealand-British physicist Ernest Rutherford (1871-1937) managed to split the nucleus of an atom by firing alpha particles at it. (Alpha particles are the nuclei of helium atoms).
Q8. What holds atoms together?
Ans. Electrons are held to the nucleus by electrical attraction- because they have an opposite electrical charge to the protons in the nucleus. The particles of the nucleus are held together by a force called the strong nuclear force.
Q7.What are electrons shells?
Electrons behave as if they are stacked around the nucleus at different levels, like the layers of an onion. These levels are called shells, and there is room for only a particular number of electrons in each shell. The number of electrons in the outer shell determines how the atom will react with other atoms. An atom with a full outer shell, like the gas argon, is unresponsive. An atom with room for one or more extra electrons in its outer shell, like oxygen, is very reactive.
Q9. What is the nucleus?
Ans. Most of an atom is empty space, but right at its center is a very tiny area that is densely packed with particles much bigger than electrons. This is the nucleus, and it usually contains two kinds of nuclear particle-neutrons with no electrical charge, and protons with a positive electrical charge (opposite to the negative charge of electrons).
Q8. What is an ion?
Ans. An ion is an atom that has either lost one or a few electrons, making it positively charged (cation) or gained a few, making it negatively charged (anions). Ions usually form when substances dissolve in a liquid.
Q7. What is a molecule?
Ans. Quite often, atoms cannot exist by themselves, and must always join up with others- either of the same chemical compounds. A molecule is the smallest particle of a substance that can exist on its own.
Q6. What are electrons?
Ans. Electrons are the very tiny electrically charged particles that whizz round inside an atom. They were discovered by the English physicist J.J. Thomson (1856-1940) in 1879 during some experiments with cathode ray tubes. (Computer and TV screens are cathode ray tubes and cathode rays are actually streams of electrons)