Atomic Structure and the Periodic table

• Atoms are made up of tiny particles called protons, neutrons, and electrons
• Protons and neutrons make up the nucleus of an atom
• Electrons orbit around the nucleus in shells
• Protons have a relative mass of one and a one plus charge
• Neutrons have a relative mass of one and no charge
• Electrons have a mass 2000 times smaller than protons and neutrons
• Electrons have a negative charge of minus one
• Atoms have a radius of around 0.1 nanometers
• Most of an atom is empty space
• The nucleus is much smaller than the atom itself
• Electrons are even smaller than the nucleus
• Atoms can become ions by losing or gaining electrons
• If an atom gains an electron, it becomes a negative ion
• If an atom loses an electron, it becomes a positive ion
• The periodic table lists different types of atoms called elements
• Each element is represented by a nucleus symbol in the periodic table
• The nucleus symbol includes the elemental symbol, atomic number, and mass number
• The atomic number represents the number of protons in an atom
• The mass number represents the total number of neutrons and protons in an atom
• The number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number
• The number of protons and electrons in an atom is always the same
• An atom is made up of a central nucleus comprising protons and neutrons, with electrons orbiting the nucleus
• The number of protons in an atom determines which element it is
• The smallest element is hydrogen with one proton in its nucleus
• Helium is the next smallest element with two protons and two neutrons in the nucleus
• There are around 100 different elements organized into the periodic table, with each box representing a different element
• The atomic number in the bottom left of the nuclear symbol represents the number of protons in the atom
• Atoms with the same number of protons but different number of neutrons are called isotopes
• Isotopes are different forms of the same element that have the same number of protons but a different number of neutrons
• Isotopes chemically react in basically the same way
• The relative atomic mass of an element is the average mass of all the isotopes that make up that element
• To calculate the relative atomic mass, you multiply each isotope's abundance by its mass, sum these figures, and divide by the sum of the abundances of all the isotopes
• For example, copper has two stable isotopes: copper 63 (69.2% abundance) and copper 65 (30.8% abundance)
• To calculate the relative atomic mass of copper, you multiply 69.2% by 63 and 30.8% by 65, sum these values, and divide by 100 (sum of abundances)
• The relative atomic mass of copper is 63.6, denoted by the symbol ar
• Molecules:

  • A group of two or more atoms held together by chemical bonds
  • Examples include oxygen, nitrogen, chlorine, and carbon dioxide
  • Can contain multiple different elements
• Compounds:

  • Substances containing two or more different elements
  • Atoms are held together by chemical bonds
  • Elements in compounds are always found in the same proportions
  • Formulas for compounds use chemical symbols and numbers for each atom
  • Examples include water (H2O), carbon dioxide (CO2), and sulfuric acid (H2SO4)
• Water:

  • Compound containing hydrogen and oxygen
  • Formula: H2O (with 2 as subscript for hydrogen)
• Carbon dioxide:

  • Compound containing oxygen and carbon
  • Formula: CO2 (with 2 as subscript for oxygen)
• Sulfuric acid:

  • Compound containing hydrogen, sulfur, and oxygen
  • Formula: H2SO4 (with 2 as subscript for hydrogen and 4 as subscript for oxygen)