A Simple Model Of The Atom
Visão Geral
Hold out your hand. Roughly a hundred different sorts of atom are enough to build everything on it, everything around it, and every star you can see at night. That is a remarkably short ingredients list for a universe. The interesting part is not how few there are, but why one sort behaves so differently from another when they are all put together from the same three tiny pieces.
This lesson takes an atom apart and puts it back together. You will place protons, neutrons and electrons where they belong, read the two numbers written beside a chemical symbol and turn them into a count of every particle inside, meet isotopes and work out why two atoms with different masses react in exactly the same way, and arrange electrons into shells for the first twenty elements. Everything you meet later in the course, from bonding to reactivity to electrolysis, is decided by where those electrons sit.
Objetivos
- All substances are made of atoms. A substance that is made of only one sort of atom is called an element. There are about 100 different elements. Elements are shown in the periodic table.
- Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen. Knowledge of the chemical symbols for elements other than those named in the specification is not required.
- Atoms have a small central nucleus, made of protons and neutrons, and around which there are electrons. Students should be aware that the atomic model has changed over time.
- The relative electrical charges are as shown: Name of particle Charge Proton +1 Neutron 0 Electron -1
- In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
- The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number. Students will be expected to calculate the numbers of each sub-atomic particle in an atom from its atomic number and mass number.
- Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
- Atoms can be represented as shown in this example: (Mass number) 23 (Atomic number) 11 Na
- Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells). Students may answer questions in terms of either energy levels or shells. Students should be able to represent the electronic structure of the first twenty elements of the periodic table in the following forms: sodium 2,8,1
- The relative masses of protons, neutrons and electrons are: Name of particle Mass Proton 1 Neutron 1 Electron Very small
- The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element. Students will not be expected to calculate relative atomic masses from isotopic abundances.
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- What is the relative charge on a neutron? A. +1 B. 0 C. -1 D. Very small Answer: B
- How many neutrons are there in one atom of potassium, written as mass number 39 and atomic number 19? A. 19 B. 20 C. 39 D. 58 Answer: B
- An atom of sulfur has an atomic number of 16. What is its electronic structure? A. 2,8,4 B. 2,8,6 C. 2,8,8 D. 2,6,8 Answer: B
- Which statement is true for two isotopes of the same element? A. They have different numbers of protons B. They have different numbers of electrons C. They have the same mass number D. They have the same atomic number but different mass numbers Answer: D
- The relative atomic mass of an element compares the mass of its atoms with a standard isotope. Which isotope is the standard? A. Hydrogen-1 B. Helium-4 C. Carbon-12 D. Oxygen-16 Answer: C
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