A chemical formula is used to represent an element or a compound in balanced chemical equations. A compound is a substance that contains two or more elements that are chemically combined. An ion is a charged particle formed when an atom or a group of atoms loses or gains electrons. The formula of an ionic compound can be predicted using its ions. The numbers of ions in a compound must give an equal number of positive and negative charges.
A pure substance consists of only one element or one compound. A mixture consists of two or more different substances, not chemically joined together. Mixtures can be separated by physical processes. These processes do not involve chemical reactions, and no new substances are made. Filtration is used to separate an insoluble solid from a liquid. It is useful for separating sand from a mixture of water, or excess reactant from a reaction mixture. Crystallisation is used to produce solid crystals from a solution. When the solution is warmed, some of the solvent evaporates leaving crystals behind. Simple distillation is used to separate a solvent from a solution. It is useful for producing pure water from seawater. Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water, and for separating different fractions from crude oil.
Ideas about atoms have changed over time. Scientists developed new atomic models as they gathered new experimental evidence. John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided. JJ Thomson carried out experiments and discovered the electron. This led him to suggest the plum pudding model of the atom. In 1909, Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil. This evidence led Rutherford to suggest a new model of the atom, called the nuclear model.
Groups in the periodic table contain different elements with similar properties. Group 0 contains non-metal elements placed in the vertical column on the far right of the periodic table. The elements in group 0 are called the noble gases. They exist as single atoms. The noble gases all have low boiling points. Group 1 contains elements placed in a vertical column on the far left of the periodic table. The elements in group 1 are called the alkali metals.
Group 7 contains non-metal elements placed in a vertical column on the right of the periodic table. The elements in group 7 are called halogens. They have seven electrons in the outer shell. Halogens are extremely reactive and readily form compounds. When halogens react with metals, they produce metal halides.
By understanding the chemical formula in balanced chemical equations, the process of separating mixtures, and the development of atomic models, we gain valuable insight into the fundamental nature of chemical compounds and the behavior of atoms and elements.
