Chemistry Unit 1

• Group 18

  • Mostly unreactive, known as Noble Gases
• Non-metals reactivity within groups

  Reactivity decreases down a group as it is harder for non-metals to attract electrons into valence shells
• Periodic Table


  Elements are the type of atom defined by their atomic number and are organized in ascending order (atomic number) to emphasize the regular repetition of chemical and physical properties
• Group 1

  • Silver, soft metals, low density, easily react with water and halogens, reactivity increases down the group, known as Alkali Metals
• Transition Metals


  Groups 3 – 12 form colourful compounds, often more than one ion, specified with a Roman numeral denoting the charge and oxidation state of the transition metal ion
• Metals reactivity across periods

  Reactivity decreases across a period as the increasing nuclear charge makes it more difficult for a metal to lose electrons
• Metals and Non-metals

  Metallic character refers to the ease with which an atom loses electrons. Metals lose electrons to become cations with the electron configuration of the previous noble gas. Non-metals gain electrons to become anions with the electron configuration of the next noble gas
• Non-metals reactivity across periods


  Reactivity increases across the period as the increasing effective nuclear charge makes it easier for a non-metallic atom
• Atomic radius decreases from le
• Groups and Periods

  Groups are vertical columns (18) and periods are horizontal rows (7) of the periodic table
• Atomic radius


  The size of an atom, measured as the distance between adjacent nuclei (in picometres) and halved
• Group 2


  • Slightly higher density, react slowly with water, known as Alkaline Earth Metals
• Elements are represented by symbols and the structure of the periodic table is based on the atomic number and the properties of the elements
• Metals reactivity within groups

  Reactivity increases down a group as it is easier for metals with a greater number of shells to lose electrons
• The group numbering scheme from group 1 to group 18, as recommended by the International Union of Pure and Applied Chemistry (IUPAC), should be used
• Group 17

  • Diatomic molecules, highly reactive with alkali metals, harmful or lethal to the environment, reactivity decreases down the group, known as Halogens
• Properties of compounds


  • Properties of compounds are different from properties of the elements they are made of
• Heterogeneous mixtures


  Have properties dependent on the identity and relative amounts of the substances that make up the mixture
• Density


  • Mass per unit volume of a substance
  • Based on the relative atomic masses of the nuclei present and how compact the atoms or ions are
• Purity of substance


  Can be established by collecting or analysing data of its physical and chemical properties, such as melting point, boiling point, and density
• Compound


  • Two or more elements whose atoms are chemically combined in a definite ratio
  • Elements in compound cannot be separated by physical change
• Element


  One type of atom
• Materials are either pure substances with distinct measurable properties (e.g. melting and boiling point, reactivity, strength, density) or mixtures with properties dependent on the identity and relative amounts of the substances that make up the mixture
• Pure Substance


  • Distinct, measurable properties that do not vary
  • Has a definite composition, contains only one type of particle
  • Can be an element or a compound
• Pure substances may be elements or compounds
• Chemical Properties


  • Characteristic of how a substance will undergo reactions to form new compounds
  • Can only be identified through experimentation
• Physical properties

  • Characteristic of a substance itself rather than its reactions
  • Can be determined without needing to undergo a chemical reaction, for example boiling and melting points, density, conductivity, colour, hardness, malleability, strength
  • Dependent upon the composition of the material
• Properties of elements and compounds

  • Substance
  • Chemical properties
  • Physical properties at 25°C
  • Water
  • Puts out fires
  • Colourless liquid
  • Boiling point: 100°C
  • Hydrogen
  • Burns explosively in air and oxygen
  • Colour gas
  • Boiling point: -253°C
  • Oxygen
  • Promotes burning
  • Colour gas
  • Boiling point: -183°C
  • Sodium chloride
  • Will not burn. Does not react with water. Does not react with hydrogen
  • White crystals. Dissolves in water. Does not conduct electricity when solid. Conducts electricity when molten
• Homogeneous mixtures


  Have distinct measurable properties such as melting and boiling point, reactivity, strength, and density
• Properties of elements

  • Each element has its own distinctive properties
  • Metals are shiny and malleable (physical)
  • Group 1 elements react violently with water
• Impurities in a substance

  Typically affect its melting and boiling points because the different compounds may have a range of melting and boiling points
• Atoms


  Can combine in different ways to produce different types of substances
• Physical or Chemical Properties

  • flammability
  • mass
  • toxicity
  • enthalpy of formation
  • elasticity
  • luster
  • heat of combustion
  • oxidation states
  • pH
  • pressure
  • viscosity
  • half-life
  • solubility
  • reactivity
  • electrical charge
• Elements in the same group

  As you move down the periodic table, the trend is increasing valency. This occurs because of the increasing number of electrons in the outermost energy level
• Atomic Radii

  • Smallest atomic radius in any period is that of the noble gas, and the largest is that of the alkali metal
• Elements that demonstrate a spike in the graph have similar properties. They may belong to the same group or have similar electron configurations
• Valency is the combining power of an element as determined by the number of electrons in its outer shell
• With each increase in atomic number, there is an increase in the number of positively charged protons so the electrostatic attraction from the protons pulls the electrons closer and the atomic radius gets slightly smaller
• With each energy level that is added to an atom, there are more electrons that need to occupy space, so the atom increases in size
• Valency

  1. Valence electrons are the electrons occupying the outermost energy level of an atom

  2. Related to the electron configuration of their atoms

  3. Normally written as the charge of the ion once the atom has gained or lost electrons to have a noble gas electron configuration

  4. Transition metals can show more than one valency, often expressed as Roman numerals