Elements, compounds and mixtures

• Matter is anything that has mass and occupies space.
• The quantity of matter in an object is its mass.
• A piece of matter in pure form is called a substance.
• Pure water is an example of a substance with the same composition and properties regardless of its source.
• Materials can be classified into pure substances (elements, compounds) and impure substances (mixtures).

Elements

• An element is a pure substance that cannot be broken down into simpler substances by ordinary physical or chemical processes.
• Gold is an example of an element.
• The fundamental unit of an element is the atom.
• Approximately 118 elements have been discovered.
• 92 elements occur naturally, while the rest are artificially prepared.
• An atom is the smallest particle of an element that can take part in a chemical reaction.
• Atoms of a particular element are the same but differ from the atoms of other elements.
• Berzelius suggested a system for representing elements with symbols in 1814.
• The shortest name of an element is called its symbol.
• In most cases, the first letter of the element's name is used as the symbol (capitalized).
• If the first letter is already in use, the initial letters or a combination of letters are used as the symbol (capitalized).

Compounds

• A compound is a pure substance consisting of two or more different types of elements chemically combined in a fixed ratio by mass.
• The component elements undergo chemical changes during compound formation.
• The properties of the compound are different from those of its constituent elements.
• Water (H₂O) is a compound of hydrogen and oxygen, with a hydrogen to oxygen atom ratio of 2:1.
• A chemical formula represents a compound, showing the symbols of the elements and their combining ratio.

Mixtures

• A mixture is made up of two or more substances that are not chemically combined.
• A mixture may consist of elements, compounds, or both.
• The components of a mixture are not in a fixed ratio.
• Mixtures can be separated by physical methods.
• The constituents of a mixture retain their characteristic properties.
• Alloys are examples of mixtures consisting of metals with other elements (metals or non-metals), such as brass and bronze.
• A homogeneous mixture has uniform composition throughout its mass.
• Table salt (NaCl) dissolved in water (solution) is a homogenous mixture.
• A heterogeneous mixture does not have uniform composition throughout; different parts have varying compositions e.g., salad.

Atomic Number and Mass Number

• Atoms consist of protons, electrons, and neutrons. Protons and neutrons are in the nucleus, while electrons revolve around it.
• The atoms of one element differ from those of other elements by the number of protons in their nuclei.
• No two elements have the same number of protons.
• Atoms are electrically neutral, thus having the same number of electrons and protons.
• The number of neutrons can vary and is not used to characterize the atom.
• The number of protons in the nucleus, called the atomic number (Z), is the basis for arranging elements in the periodic table.
• Atomic Number (Z) = Number of protons = Number of electrons in an atom.
• Hydrogen, carbon, and oxygen have one, six, and eight protons in their nuclei, respectively, corresponding to their atomic numbers.

Relative Atomic Mass and Atomic Mass Unit

• Measuring atomic mass in grams or kilograms results in extremely small values (10-24 to 10-22 g).
• Atomic masses are expressed by comparing them to the mass of a standard atom, which is carbon-12 (mass of exactly 12 units).
• The relative atomic mass of an element is the mass of an atom relative to 1/12 the mass of C-12.
• Atomic mass unit (a.m.u.) is defined as 1/12 the mass of a carbon-12 atom.

Average Atomic Mass

• Atomic masses are often not whole numbers because most elements are composed of two or more naturally occurring isotopes.
• The average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element.

Chemical Formulas

• Chemical formulas represent compounds.
• They are created by combining the chemical symbols of the elements, with their relative ratios by the number of atoms.
• A chemical formula is an abbreviation for the full name of a compound, using symbols.
• It represents the symbolic representation of a molecule of a compound.
• The chemical formula indicates the types of atoms (elements) present in the compound.
• The chemical formula indicates the ratio of the different atoms present in the compound.
• Sodium Nitrate is NaNO₃
• Glucose is C₆H₁₂O₆

Empirical and Molecular Formula

• The empirical formula is the simplest formula, showing the smallest whole number ratio of atoms of different elements.
• The empirical formula may not be the actual formula of the compound.
• Benzene (C₆H₆) has a simplest ratio of 1:1, so its empirical formula is CH.
• Glucose (C₆H₁₂O₆ ) has a simplest ratio of 1:2:1, so its empirical formula is CH₂O.
• The molecular formula shows the actual number of atoms of different elements present in one molecule.
• Molecular Formula of Glucose is C₆H₁₂O₆
• Molecular Formula of Benzene is C₆H₆
• Molecular formula = n (Empirical Formula).
• Where n = 1, 2, 3, 4.....
• Molecular formula of benzene is Molecular formula = 6 (CH)
• Molecular formula = C₆H₆.

Branches of Chemistry

• Physical Chemistry: Deals with relationship between physical properties of substances and chemical changes.
• Organic Chemistry: Study of compounds containing carbon and hydrogen (hydrocarbons) and their derivatives.
• Inorganic Chemistry: Study of all elements and compounds except hydrocarbons and their derivatives.
• Analytical Chemistry: Study of qualitative (type/kind) and quantitative (amount/nature) analysis of matter.
• Industrial Chemistry: Study of techniques and chemical processes for preparation of industrial products (e.g., cement, glass, fertilizers).
• Nuclear Chemistry: Study of nucleus, changes occurring in nucleus, properties of particles in nucleus, and emission/absorption of radiation.
• Biochemistry: Study of synthesis, composition, decomposition, and chemical reactions of substances in living organisms.
• Environmental Chemistry: Study of interaction of chemical substances/processes with environment and their impact.