Chem

• What does the electronic structure of an atom describe?


  The arrangement of electrons in an atom
• What subatomic particles are found in the nucleus of an atom?

  Positive protons and neutral neutrons
• Where are the negative electrons located in an atom?

  In energy shells or energy levels surrounding the nucleus
• What is the relative mass of protons and neutrons compared to electrons?

  Protons and neutrons have a relative mass of 1, while electrons have a relative mass of almost 0
• Why is understanding the electronic structure of atoms important for lab technicians?

  It allows them to predict how chemical substances will behave and react
• What is the structure of an atom?

  • Nucleus at the center containing protons and neutrons
  • Electrons in shells or energy levels surrounding the nucleus
  • Each shell can hold a maximum number of electrons
  • Electrons fill the first shell before moving to the second, and so on
  • Table 1.1 shows the maximum number of electrons in each shell
• What is the electron arrangement of a sodium atom with 11 electrons?

  2, 8, 1
• What are the energy levels or shells in an atom according to Bohr’s theory?

  • Imagine as orbiting circles around the nucleus
  • Each shell can hold a maximum number of electrons
• What are orbitals?

  • Sub-shells within each energy level
  • Called s, p, d, and f orbitals
  • Have different energy states
  • Each orbital can hold a maximum of two electrons
• What is the maximum number of electrons an orbital can hold?

  Two electrons
• What are orbitals?

  Regions where there is a 95% probability of locating an electron
• What is the Aufbau principle?

  • States that electrons fill orbitals with the lowest available energy state closest to the nucleus
  • Then fill orbitals with higher energy states
  • This results in the most stable electron configuration possible
• How do electrons fill orbitals in an energy level?

  • Electrons have the same charge and repel each other
  • If more than one orbital is in an energy level, they are filled singly
  • Once all orbitals have an electron, they then pair up
• What is electron configuration?

  The distribution of electrons in an atom or molecule
• What are the possible spin states of an electron?

  • Spin up
  • Spin down
• In an orbital, how many electrons will have different spin states?

  Each electron will be in a different spin state
• What are the electronic structures for helium, boron, and carbon?

  Helium: $1s^2$

  Boron: $1s^2\,2s^2\,2p^1$

  Carbon: $1s^2\,2s^2\,2p^2$
• What is the electronic structure of oxygen?

  $1s^2\,2s^2\,2p^4$
• What is new compared to Key Stage 4 about electronic structure?

  • Introduction to orbitals (s, p, d, f) and their energy states
  • Filling orbitals according to Hund’s rule
  • Understanding the spin of electrons
  • Exploring covalent bonding including dative bonds
  • Tetrahedral structures in organic compounds
• Why must lab technicians know what type of compound they are using?

  • To use the correct solvent as different types of compounds dissolve in different solvents based on their bonding
• What is ionic bonding?

  • Occurs between atoms of a metal and a non-metal
  • An atom loses one or more electrons and donates them to another atom
  • The atom that loses electrons becomes positively charged (cation)
  • The atom that gains electrons becomes negatively charged (anion)
  • Imbalance of protons and electrons creates the charges
  • Opposite charges attract, forming the ionic bond
• What is ionic bonding?

  Electrostatic attraction between two oppositely charged ions
• How can ionic bonding in sodium chloride be represented using a dot and cross diagram?

  • Sodium (Na) loses one electron to become $Na^+$
  • Chlorine (Cl) gains one electron to become $Cl^-$
  • Electrons are represented by dots and crosses
  • Electrons fill shells singly and then in pairs
• What type of ions can also be formed in ionic bonding?

  • Polyatomic ions containing more than one element
  • Example: $OH^-$ in sodium hydroxide $(Na^+$OH^-)</latex>
• What holds ions together in an ionic compound?

  Electrostatic attraction
• What structure is formed by oppositely charged ions in an ionic compound?

  A giant ionic lattice
• On what factors does the strength of ionic bonds depend?

  • Ionic charge: Stronger with higher ionic charges
  • Ionic radii: Weaker with larger ionic radii as charge is spread over larger area
  • Number of shells: More shells lead to larger radii and weaker bonds
• Define electrostatic attraction and giant ionic lattice.

  Electrostatic attraction: The force experienced by oppositely charged particles; holds them strongly together

  Giant ionic lattice: A regular arrangement of positive and negative ions in a compound
• What is covalent bonding?

  • Usually occurs between atoms of two non-metals
  • Involves sharing electrons between the atoms
  • Shared electrons come from the highest energy levels
• From which energy level do the shared electrons in covalent bonding originate?

  From the top energy level of the atoms
• How does covalent bonding lead to stable electron configurations in chlorine molecules?

  • Each chlorine atom has seven electrons in the highest shell
  • One electron from each atom is shared to give each atom eight electrons
  • This gives each atom the electron configuration of argon (a noble gas)
  • Both atoms have a stable full outer shell
• What is dative (coordinate) covalent bonding?

  When both sharing electrons come from one atom
• Explain dative covalent bonds in oxygen molecules.

  • Double bonds formed between oxygen atoms
  • Each bond involves two shared pairs of electrons
  • One oxygen atom donates both pairs of electrons
• What type of bond is formed when three pairs of electrons are shared?

  A triple covalent bond
• What is a lone pair?

  A non-binding pair of electrons
• How does a dative bond form in the ammonium ion?

  • When ammonia $(NH_3)$ reacts with hydrochloric acid
  • A hydrogen ion $(H^+)$ from the acid is transferred to the ammonia
  • A lone pair of electrons on the nitrogen atom forms a dative covalent bond with $H^+$
• How does the length of single, double, and triple bonds compare?

  Single bonds > double bonds > triple bonds
• What relationship exists between bond length and bond strength?

  The shorter the bond length, the stronger the bond
• How many covalent bonds does carbon make?

  Four covalent bonds
• What is the formula for methane?

  $CH_4$