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Chemistry is the study of matter and how it changes. It includes different areas such as organic chemistry, which looks at carbon-containing compounds, and inorganic chemistry, which studies compounds without carbon. Physical chemistry studies the physical properties of substances, while analytical chemistry analyzes what substances are made of. Biochemistry studies chemical processes in living things. For example, chemistry helps us understand how water behaves or how photosynthesis works.

The basic atomic structure is made up of protons, neutrons, and electrons. Protons determine the atomic number of an element, neutrons contribute to its atomic mass and create isotopes, and electrons are involved in chemical bonding. For instance, an oxygen atom has 8 protons, 8 neutrons, and 8 electrons, giving it an atomic number of 8 and an atomic mass of 16 amu.

The Periodic Table organizes elements by their atomic number and chemical properties, arranged in rows and columns. Key trends in the table include electronegativity, which increases across rows and decreases down columns; ionization energy, which also increases across rows and decreases down columns; and atomic size, which decreases across rows and increases down columns. Understanding the Periodic Table helps predict how elements will behave in chemical reactions.

Chemical bonds are connections that hold atoms together to form molecules and compounds. There are three main types: ionic bonds, which involve the transfer of electrons between a metal and a nonmetal; covalent bonds, which involve the sharing of electrons between two nonmetal atoms; and metallic bonds, where electrons form a "sea" around metal atoms, allowing them to conduct electricity. Understanding chemical bonding helps explain the properties of different substances.

A chemical reaction is when substances change into new ones, and a chemical equation shows this change mathematically. A balanced equation has the same number of atoms on both sides, ensuring that mass is conserved.

Matter exists in three main states: solid, liquid, and gas. Each state has unique characteristics. Temperature changes can cause matter to change states through melting (solid to liquid), boiling or evaporation (liquid to gas), condensation (gas to liquid), freezing (liquid to solid), sublimation (solid to gas), and deposition (gas to solid). These changes depend on energy input or output and are influenced by the kinetic energy of the particles. For example, heating ice causes it to melt into liquid water, which can then boil into steam at a higher temperature.

Acids are substances that release hydrogen ions in water, have a pH less than 7, taste sour, and corrode metals. Bases release hydroxide ions, have a pH greater than 7, taste bitter, feel slippery, and neutralize acids. Common acids include hydrochloric acid and citric acid, while common bases include sodium hydroxide and ammonia.

A solution is a mixture where a solute dissolves in a solvent. Solubility is how well a solute dissolves in a solvent and is affected by temperature, pressure, and polarity. For example, salt dissolves in water to form a salt water solution.

Stoichiometry is using balanced chemical equations to find out the amounts of reactants and products in a chemical reaction. To do this, you balance the chemical equation, use mole ratios, and convert between grams and moles. For example, in the reaction CH4+2O2→CO2+2H2OCH4+2O2→CO2+2H2O, 16 grams of methane react with oxygen to produce 44 grams of carbon dioxide.

Thermodynamics in chemistry is the study of heat and energy changes during chemical reactions and physical changes. A key concept is Gibbs free energy, which can be calculated using the formula ΔG=ΔH−TΔSΔG=ΔH−TΔS, where TT is the temperature in Kelvin.