Atoms, elements, compounds, chemical equations

• What are atoms made of?

  Atoms are made of protons, neutrons, and electrons.
• How small are atoms compared to visible objects?

  Atoms are too small to see, even with a microscope.
• What is located in the nucleus of an atom?

  The nucleus contains protons and neutrons.
• Why does the nucleus have a positive charge?

  The nucleus has a positive charge because of the protons it contains.
• Where is most of the mass of an atom concentrated?

  Almost the whole mass of the atom is concentrated in the nucleus.
• What is the relative mass and charge of a proton?

  A proton has a relative mass of 1 and a charge of +1.
• What is the relative mass and charge of a neutron?

  A neutron has a relative mass of 1 and a charge of 0.
• What is the relative mass and charge of an electron?

  An electron has a very small relative mass and a charge of -1.
• How do electrons move in an atom?

  Electrons move around the nucleus in electron shells.
• What determines the size of an atom?

  The size of the electron orbits determines the size of the atom.
• Why are atoms neutral?

  Atoms are neutral because they have the same number of protons as electrons.
• What happens to the charges of protons and electrons in an atom?

  The charge on the electrons is the same size as the charge on the protons, but opposite.
• What defines an element?

  An element is a substance made up of atoms that all have the same number of protons in their nucleus.
• What determines the type of atom?

  The number of protons in the nucleus determines what type of atom it is.
• What is the atomic number of hydrogen?

  The atomic number of hydrogen is 1, meaning it has one proton.
• What is the atomic number of helium?

  The atomic number of helium is 2, meaning it has two protons.
• What is the relationship between the number of protons and the number of electrons in an element?

  All the atoms of a particular element have the same number of protons and different elements have atoms with different numbers of protons.
• How can atoms be represented?

  Atoms can be represented by one or two letter symbols.
• What is an example of a symbol for an element?

  C represents carbon, O represents oxygen, and Mg represents magnesium.
• What are isotopes?

  Isotopes are different forms of the same element with the same number of protons but a different number of neutrons.
• How do isotopes differ from each other?

  Isotopes have the same atomic number but different mass numbers.
• What is a popular example of isotopes?

  A popular example of isotopes is carbon-12 and carbon-13.
• What is relative atomic mass (Ar)?

  Relative atomic mass (Ar) is an average mass taking into account the different masses and abundances of all the isotopes that make up the element.
• How do you calculate the relative atomic mass of an element?

  Relative atomic mass (Ar) = sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes.
• What is the relative atomic mass of copper with isotopes Cu-63 and Cu-65?

  The relative atomic mass of copper is $63.6$.
• What are the differences between atoms, elements, and isotopes?

  • Atoms: Basic units of matter made of protons, neutrons, and electrons.
  • Elements: Substances made of atoms with the same number of protons.
  • Isotopes: Different forms of the same element with the same number of protons but different numbers of neutrons.
• What happens when elements react to form compounds?

  When elements react, they combine with other atoms to form compounds.
• What are compounds made of?

  Compounds are substances formed from two or more elements in fixed proportions.
• What holds the atoms together in a compound?

  Atoms in a compound are held together by chemical bonds.
• What happens to the nuclei of atoms when a bond is made?

  The nuclei of the atoms aren’t affected when a bond is made; only the electrons are involved.
• How are compounds formed from metals and non-metals different from those formed from non-metals?

  A compound formed from a metal and a non-metal consists of ions, while a compound formed from non-metals consists of molecules.
• What is ionic bonding?

  Ionic bonding occurs when metal atoms lose electrons to form positive ions and non-metal atoms gain electrons to form negative ions.
• What is covalent bonding?

  Covalent bonding occurs when atoms share electrons.
• How do the properties of a compound compare to the properties of the original elements?

  The properties of a compound are usually totally different from the properties of the original elements.
• What does a formula show in a compound?

  A formula shows what atoms are in a compound and their proportions.
• What is the formula for carbon dioxide?

  The formula for carbon dioxide is CO₂.
• What is the formula for sulfuric acid?

  The formula for sulfuric acid is H₂SO₄.
• What do brackets in a formula indicate?

  Brackets in a formula indicate that the little number outside applies to everything inside the brackets.
• What is the formula for calcium hydroxide?

  The formula for calcium hydroxide is Ca(OH)₂.
• What are some examples of chemical formulas for compounds?

  1. Carbon dioxide – CO₂
  2. Ammonia – NH₃
  3. Water – H₂O
  4. Sodium chloride – NaCl
  5. Carbon monoxide – CO
  6. Hydrochloric acid – HCl
  7. Calcium chloride – CaCl₂
  8. Sodium carbonate – Na₂CO₃
  9. Sulfuric acid – H₂SO₄