Elements, Compounds, and Mixtures

Elements, Compounds, and Mixtures

• An element is a pure substance composed of only one type of atom.
• Elements cannot be broken down into simpler substances.
• Elements are represented by chemical symbols, such as O for oxygen or H for hydrogen.
• Examples of elements: oxygen (O2), carbon (C)
• A compound is formed when two or more different elements chemically combine.
• Compounds have distinct and unique properties different from the elements that make them up.
• Compounds can be represented by chemical formulas, such as H2O for water or CO2 for carbon dioxide.
• Compounds cannot be separated physically; chemical reactions are needed to break them down into their individual elements.
• Examples of compounds: water (H2O), carbon dioxide (CO2)
• A mixture is a combination of two or more substances (elements or compounds) physically mixed together but not chemically bonded.
• The components in a mixture retain their individual properties and can be separated by physical means, such as filtration or distillation.
• Example: Salt water

Atoms and Subatomic Particles

• An atom is the smallest unit of matter that makes up everything around us.
• Atoms are the basic building blocks of all substances.
• Atoms consist of subatomic particles: protons, neutrons, and electrons.
• The nucleus is the central core of an atom, containing protons and neutrons.
• Protons are positively charged particles found in the nucleus.
• Neutrons are neutral particles (no charge) also found in the nucleus.
• Electrons are negatively charged particles that orbit the nucleus in specific energy levels or shells.
• Electrons are much lighter than protons and neutrons.

Atomic Structure

• The atomic number (represented by Z) is the number of protons in the nucleus of an atom.
• The number of protons always equals the number of electrons in a neutral atom.
• The atomic number helps identify an element's location on the periodic table.
• The mass number (represented by A) is the total number of protons and neutrons in the nucleus of an atom.
• The mass number represents the total mass of the atom.
• The mass number is equal to the number of protons plus the number of neutrons.
• Relative atomic mass is the average mass of all the isotopes of an element, rounded to the nearest whole number for simplicity.
• The mass number is close to the relative atomic mass, and for most elements, the relative atomic mass can be used as a substitute for the mass number.
• The number of neutrons can be calculated by subtracting the atomic number from the mass number.

Periodic Table

• The periodic table lists elements with their atomic number at the top and the relative atomic mass at the bottom.