Atomic Structure and Elements

Atomic Structure

• An atom is the smallest unit of a chemical element that retains the properties of that element.
• Atoms consist of:
  • Protons: positively charged particles in the nucleus (center) of the atom.
  • Neutrons: particles with no charge in the nucleus.
  • Electrons: negatively charged particles orbiting the nucleus.

Elements

• An element is a substance that consists of only one type of atom.
• Elements are represented by a unique symbol (e.g., H for Hydrogen, C for Carbon).
• Elements can exist in different forms, called isotopes, which have the same number of protons but a different number of neutrons.

Molecules

• A molecule is a group of two or more atoms chemically bonded together.
• Molecules can be composed of atoms from the same element (e.g., O2) or different elements (e.g., H2O).
• Molecules have a fixed ratio of atoms, which is represented by a chemical formula (e.g., H2O for water).

Compounds

• A compound is a substance formed by the chemical combination of two or more different elements.
• Compounds have a fixed ratio of atoms, which is represented by a chemical formula.
• Compounds have properties that are different from their individual component elements.

Key Concepts

• Chemical bond: a force that holds atoms together in a molecule or compound.
• Chemical formula: a notation that represents the ratio of atoms in a molecule or compound.
• Molecular weight: the sum of the atomic weights of all atoms in a molecule or compound.

Examples

• Element: Oxygen (O)
• Molecule: Oxygen molecule (O2)
• Compound: Water (H2O)
• Molecule composed of different elements: Carbon dioxide (CO2)

Atomic Structure

• An atom is the smallest unit of a chemical element that retains its properties.
• Atoms consist of protons, neutrons, and electrons, with protons and neutrons in the nucleus and electrons orbiting around it.

Elements

• An element is a substance made up of only one type of atom.
• Each element has a unique symbol, such as H for Hydrogen and C for Carbon.
• Elements can exist in different forms called isotopes, which have the same number of protons but a different number of neutrons.

Molecules

• A molecule is a group of two or more atoms chemically bonded together.
• Molecules can be made up of atoms from the same element or different elements.
• The ratio of atoms in a molecule is represented by a chemical formula, such as H2O for water.

Compounds

• A compound is a substance formed by the chemical combination of two or more different elements.
• Compounds have a fixed ratio of atoms, which is represented by a chemical formula.
• Compounds have properties that are different from their individual component elements.

Key Concepts

• A chemical bond is a force that holds atoms together in a molecule or compound.
• A chemical formula is a notation that represents the ratio of atoms in a molecule or compound.
• Molecular weight is the sum of the atomic weights of all atoms in a molecule or compound.

Examples

• Oxygen is an element with the symbol O.
• Oxygen molecule (O2) is an example of a molecule made up of atoms from the same element.
• Water (H2O) is an example of a compound made up of hydrogen and oxygen atoms.
• Carbon dioxide (CO2) is an example of a molecule made up of atoms from different elements.