(元素)周期表
WordDefinitionTopicalkali metalsThe alkali metals are the elements in Group 1 of
| Word | Definition | Topic |
|---|---|---|
| alkali metals | The alkali metals are the elements in Group 1 of the periodic table. They have one electron in the outer shell. | The periodic table |
| atom | All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. | The periodic table |
| atomic number | The atomic number (Z) of an element is the number of protons in the nucleus of the atom. | The periodic table |
| atoms | All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. | The periodic table |
| boiling point | The temperature at which a liquid changes its state to gas. | The periodic table |
| brittle | If something is brittle it is easily broken. | The periodic table |
| catalyst | A catalyst changes the rate of a chemical reaction without being changed by the reaction itself. | The periodic table |
| catalytic converter | A device in internal combustion engines which catalyses reactions converting harmful exhaust gases such as carbon monoxide into normal atmospheric gases. | The periodic table |
| compound | A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. | The periodic table |
| conduct | To allow electricity, heat or other energy forms to pass through. | The periodic table |
| conductor | An electrical conductor is a material which allows an electrical current to pass easily. It has a low resistance. A thermal conductor allows thermal energy to be transferred through it easily. | The periodic table |
| covalent bond | A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. | The periodic table |
| displacement reactions | Displacement reactions happen when a more-reactive element replaces a less-reactive element in a compound. | The periodic table |
| electron | An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. | The periodic table |
| element | All atoms of an element have the same atomic number, the same number of protons and electrons and so the same chemical properties. | The periodic table |
| groups | The groups of elements in the periodic table are the elements which have the same number of electrons in their outer shells and so have similar chemical properties. A group of elements all lie in same column in the periodic table. | The periodic table |
| halogens | The halogens are the elements in Group VII of the periodic table. They have seven electrons in the outer shell. | The periodic table |
| ionic compound | An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). The ions swap electrons to achieve a full outer shell. | The periodic table |
| molecular compound | A molecular compound is made up of at least two different elements, which share electrons to form covalent bonds. | The periodic table |
| molecule | A molecule is a collection of two or more atoms held together by chemical bonds. It is the smallest part of a substance that displays the properties of the substance. | The periodic table |
| nucleus | Found at the centre of an atom, the nucleus contains protons and neutrons. | The periodic table |
| noble gases | The noble gases are the elements in Group 0/Group VIII of the periodic table. They have a full outer shell of electrons and so are unreactive. | The periodic table |
| periods | The periods of elements in the periodic table are the elements in which the same outer shell is being filled up. A period of elements in the periodic table all lie in the same row. | The periodic table |
| radioactive | A radioactive isotope gives off (or is capable of giving off) radiant energy in the form of particles or rays by the spontaneous disintegration of the nucleus. | The periodic table |
| relative atomic mass | The relative atomic mass is the number of times heavier an atom is compared to one twelth of a carbon-12 atom. | The periodic table |
| vapour | Vapour is a cloud of liquid particles. Steam is water vapour. | The periodic table |
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