Year 10 Chemistry Revision Complete Solutions

Year 10 Chemistry Revision Complete Solutions Elements, Molecules, and Compounds In its purest form, an element consists of atoms with the same composition. A molecule is formed when two or more atoms, identical or different, bond together. A compound, on the other hand, is created when two or more different atoms combine in a fixed ratio. Atoms and Ions The smallest particle of matter with a consistent composition is an atom. An ion is formed when an atom loses or gains an electron, resulting in an overall charge. Isotopes are variations of elements that have the same number of protons but differ in the number of neutrons. Physical and Chemical Changes Physical changes are reversible transformations that involve a change in state. For example, solid-to liquid (ice to water) or solid-to-gas (dry ice to CO2 gas) transformations do not alter the molecular structure. In contrast, chemical changes are irreversible processes that involve the formation of new compounds with distinct properties and appearances. These changes are often marked by color changes, fizzing or gas release, or odor emission. Key Takeaways * Elements are substances with identical atoms. * Molecules are formed by combining identical or different atoms. * Compounds result from combining different atoms in a fixed ratio. * Atoms can become ions by gaining or losing electrons. * Isotopes differ in neutron count despite having the same number of protons. * Physical changes are reversible and do not alter molecular structure, whereas chemical changes are irreversible and form new compounds. Alkali Metals ️Group one of the periodic table. They react with water to form alkaline solutions. They form +1 ions and are very reactive. They must be stored under oil. The are low in density, conduct electricity, are malleable and are shiny. Alkaline Earth Metals ️Group two of the periodic table. They are extracted from oxides on the Earth's crust. They are less reactive that group one. They form +2 ions, conduct electricity, are malleable and shiny. Halogens ️Group seven of the periodic table and are very reactive. They don't occur free in nature but as diatomic molecules. They combine with metals to form ionic salts. The states at r