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| Science |
| Biology and Chemistry assignments can be found on GAVirtualSchool.org |
| The Chemical and Molecular: Basis of Life The Elements- Element- a substance which cannot de decomposed into simpler or less complex substance by ordinary chemical means. Compound- a combination of elements present in definite proportions by weight. These are substances which can be decomposed by chemical means. Mixtures- contain two or more substances, each of which retains its original properties and can be separated from the others by relatively simple means. They do not have a definite composition. Atoms- Each element is made up of one kind of atom. An atom is the smallest part of an element which can combine with other elements. Each Atom Consists of: A). Atomic Nucleus- small, dense center of an atom B). Proton- positively charged particle of the nucleus C). Neutron- electrically neutral particle of the nucleus D). Electron- negatively charged particle which orbits the nucleus In normal, neutral atoms, the number of electrons is equal to the number of protons. Atomic Weight- The total number of protons and neutrons in a nucleus is the atomic weight (mass number). This number approximates the total mass of the nucleus. Atomic Number- The atomic number is equal to the number of protons in the nucleus of an element. Isotope- Atoms of the same element that have a different number of neutrons are known as isotopes. All isotopes of the same element have essentially the same chemical properties but their physical properties may be affected. Ions- Atoms or groups of atoms which have lost or gained electrons are called ions. One of the ions formed is always electrically positive and the other electrically negative. Sample Questions: Question: Describe the difference between an element and a compound. Answer: All substances are composed of matter, which means that they have mass and occupy space. Elements and compounds constitute two general classes of matter. Elements are substances that consist of identical atoms (atoms with identical atomic numbers). This definition of an element includes all isotopes of that element. Hence O^18 and O^16 are both considered to be elemental oxygen. A compound is a substance that is composed of two or more different kinds of atoms (two or more different elements) combined in a definite weight ratio. This fixed composition of various elements, according to the law of definite proportions, differentiates a compound from a mixture. Elements are the substituents of compounds. For example, water is a compound composed of two elements of hydrogen and oxygen in the ratio 2:1, (two to one), respectively. This compound may be written as H2o, |
