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15 Cards in this Set
- Front
- Back
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Chemical Changes
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A chemical change occurs when a new substance is formed. 2 or more changes have occurred to say it's a chemical change.
- gas given off - colour change - different smell - heat given out or absorbed - change cannot be easily reversed |
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Physical Changes
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Not a permanent change.
- substance changes states (solid to liquid) - change can be easily reversed. - no new substances are formed - mass of object same at the end of change |
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Atoms
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Everything is made from atoms. Tiny particles, too small to see. Electrons, protons, neutrons. Atomos- indivisible in Greek.
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Electrons
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Tiny particles that have a negative electrical charge. (-) the y orbit the centre of the atom (nucleus) electrons are 2000x smaller then protons and neutrons.
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Protons
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Subatomic particle. Larger and heavier then electrons, have a positive charge (+). Found inside nucleus.
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Neutrons
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Subatomic particle. Large and have a similar mass to protons. No electrical charge (0). Present in all atomic nuclei except hydrogen.
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Elements
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A substance made of only one type of atom is called an element. Cannot be broken down into simpler substances, are primary constitutes of matter. Each element has a symbol, starts with a capital, derived from it's name. Some elements retain the symbol based in heir Latin name.
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Getting to know the Periodic Table
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The # at the top = atomic number, represent number of protons found in the nucleus of the atom or the electrons orbiting that element. The big number is the atomic mass, tells us the mass of a single atom. Made up of protons and neutrons, electrons have no mass to contribute.
Atomic mass - atomic number = number of neutrons. |
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Closer look at Electrons
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Electrons tell us if two chemicals are going to react. They are arranged in orbiting shells, layers. The first shell can only hold two electrons. The second shell can only hold 8, the third shell can only hold 8. Outermost shell = valence. They like to be in pairs.
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Role of the Electron
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During chemical reaction, atom wants to get a full outer a of electrons, it can do this by losing it gaining electrons and forming an ion. Ion is a atom with an electrical charge. Metals tends to lose electrons to become positive ions, Na-->Na+1. Non metals tend to gain electrons to become negative ions, Cl-->Cl-1. Electrons are lost or gained to make to allow the element to become a more stable form. The single valence electrons of each ion meet in a common space to produce a pair of electrons that are shared between ions. This creates a chemical bond which forms a compound.
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Trends in the Periodic Table
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There are 18 groups that are columns (down) of element with similar chemical properties. Groups run from left to right and are numbered 1,2,3..18. Column 1-12 = metals column 3-12 = transition metals, column 13-18 = non metals. Group 1 metals are alkali metals. Group 17 elements are halogens, group 18 elements are noble (inert) gases. There are 7 periods (rows) of elements that increase in atomic number and mass from left to right. Period run from too to bottom= 1,2,3,4,5,6,7
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Mixtures
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Combined but not chemically joined. The product or the random distribution of one substance through without any chemical reaction, as distinct from a compound.
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Compound
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A substance made of two or more different elements chemically bonded.
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Molecule
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Two of the same element are chemically bonded.
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Balancing symbol equations
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Matter cannot be created or destroyed- law of conservation of mass. The number of atoms in the reactants will always equal the number of atoms in the products. Monotonic ion- ion consisting of a single atom e.g. Na+, Au+3
Polyatomic ion- consists of more then one element e.g. SO4-2, NO3- |
