Atomic Structure
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Press your hand flat on the table. It stops. Nothing sinks in, nothing passes through, and the surface feels as solid as anything in the world. Yet if you could shrink until a single atom of that table filled a school sports hall, the part of it that carries virtually all the weight would be one grain of sand hovering at the centre circle, and everything else in the hall would be empty. That is not a poetic exaggeration. It is what your specification asks you to believe about matter, in one sentence, on the first line of this topic.
You will start with two radii, the atom's and its nucleus's, and find out how astonishingly far apart they are. Then you will meet the three particles by their relative masses and charges, count them for any atom you are handed, turn atoms into ions by taking electrons off them, and learn to read the notation that packs a whole nucleus into two small numbers beside a chemical symbol. Extension Tier candidates go one step further and meet the experiment that proved the model was right in the first place. By the end you will be able to look at any symbol, any table of particles or any pair of isotopes and say exactly what is in front of you.
Objetivos
- Atoms are very small, having a radius of about 10-10 metres. The simple model of an atom is a small central positively charged nucleus composed of protons and neutrons, surrounded by electrons. The radius of the nucleus is much smaller than that of the atom with almost all of the mass in the nucleus.
- The scattering of alpha particles by thin metal foil provides evidence of the distribution of mass in the atom.
- The relative masses and electric charges of protons, neutrons and electrons are as follows: Relative mass Relative charge Proton 1 1 Neutron 1 0 Electron Very small -1
- In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no overall electrical charge.
- In each atom its electrons are arranged at various distances from the nucleus. Atoms may lose or gain outer electrons to form charged particles called ions.
- The atoms of a particular element always have the same number of protons, but have a different number of neutrons for each isotope. The total number of protons in an atom is called its proton number or atomic number. The total number of protons and neutrons in an atom is called its mass number. Atoms can be represented as shown: (Mass number) 23 (Atomic number) 11 Na
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- Which particles are found in the nucleus of an atom? A. Protons and electrons B. Neutrons and electrons C. Protons and neutrons D. Protons, neutrons and electrons Answer: C
- What is the approximate radius of an atom? A. 10^-6 m B. 10^-10 m C. 10^-15 m D. 10^-20 m Answer: B
- Which statement about the nucleus of an atom is correct? A. Its radius is about the same as the radius of the atom B. It contains almost all of the mass of the atom C. It has no overall electrical charge D. It contains the electrons Answer: B
- An atom of an element has 19 protons, 20 neutrons and 19 electrons. It then loses one electron. What is the overall charge on the particle formed? A. -1 B. 0 C. +1 D. +19 Answer: C
- Two atoms are isotopes of the same element. Which quantity must be the same for both? A. The number of neutrons B. The number of protons C. The mass number D. The total number of particles in the nucleus Answer: B
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