Chem unit 1

• What are atoms in relation to elements?

  Atoms are the smallest part of an element
• How are elements represented in symbols?

  By capital letters, sometimes lowercase
• How many different elements are there approximately?

  About 100 different elements
• What does the periodic table show?

  The elements and their symbols
• What is the difference between compounds and mixtures?

  • Compounds: chemically combined elements in fixed proportions
  • Mixtures: elements or compounds not chemically combined
• What happens during a chemical reaction involving compounds?

  Energy is released or absorbed
• How many oxygen atoms are in a molecule of carbon dioxide?

  Two oxygen atoms
• What is the ratio of hydrogen to oxygen in water?

  Two hydrogen to one oxygen
• What is the word equation for sodium reacting with chlorine?

  Sodium + Chlorine → Sodium Chloride
• What does a balanced equation represent?

  Equal number of each atom on both sides
• What is the maximum number of electrons in the first shell of an atom?

  Two electrons
• What is the purpose of filtration in separating mixtures?

  To separate insoluble solids from liquids
• What does crystallization achieve in a mixture?

  Separates soluble solids from solvents
• What is the role of the condenser in simple distillation?

  To cool and condense vapor back to liquid
• What does chromatography separate?

  Inks or pigments from mixtures
• What was the plum pudding model of the atom?

  Electrons embedded in a positive charge ball
• What did the alpha particle scattering experiment reveal?

  Most of the atom is empty space
• What is the nuclear model of the atom?

  Positively charged nucleus with orbiting electrons
• Who proposed that electrons orbit the nucleus at specific distances?

  Neils Bohr
• What is the charge of a proton?

  +1
• Where are neutrons located in an atom?

  In the nucleus
• What is the relative mass of an electron?

  Very small compared to protons
• How do you determine the number of neutrons in an atom?

  Mass number minus atomic number
• What is an isotope?

  Atoms with the same protons, different neutrons
• How do you calculate relative atomic mass from isotopes?

  Using abundance and mass numbers
• What are the methods for separating mixtures?

  • Filtration
  • Crystallization
  • Simple distillation
  • Fractional distillation
  • Chromatography
• What are the key features of the nuclear model of the atom?

  • Positively charged nucleus
  • Electrons orbiting the nucleus
  • Mostly empty space in the atom
• What are the relative charges and masses of subatomic particles?

  • Proton: +1 charge, mass 1
  • Neutron: 0 charge, mass 1
  • Electron: -1 charge, very small mass
• What is the electronic structure of sodium?

  • Protons: 11
  • Electrons: 11
  • Neutrons: 12
  • Electronic configuration: 2, 8, 1
• What is the significance of isotopes in chemistry?

  • Same chemical properties
  • Different physical properties
• What is the formula for calculating relative atomic mass?

  Relative atomic mass = (abundance1 × mass1 + abundance2 × mass2) / 100
• What do isotopes have in common?

  Same number of protons
• How do isotopes differ from each other?

  Different number of neutrons
• What properties do isotopes share?

  Same chemical properties
• What is the formula for calculating relative atomic mass?

  Percentage abundance times relative atomic mass
• What is the relative atomic mass of chlorine?

  35.5
• How were elements arranged before the discovery of subatomic particles?

  By atomic weight
• What pattern was noticed in early periodic tables?

  Every eighth element had similar properties
• What did Mendeleev do differently in his periodic table?

  Left gaps for undiscovered elements
• Why was the order based on atomic weight sometimes incorrect?

  Knowledge of isotopes explained discrepancies