Chapter 1 Flashcards
Atomic Structure
- Dalton - Solid Spheres
- Thomson - Electrons
- Rutherford - Nucleus
- Chadwick - Neutrons
- Bohr - Energy Levels
- Schrödinger - Electron Clouds
Octet Rule
- Atoms are stable when the valence shell is full
- For many common elements they are stable with 8 electrons so this is generalized with the octet rule
- Atoms will form bonds or ions to achieve a complete valence shell
Cations
+
- Cations form when an atom loses its electrons
- Metals form cations
- The energy required to “lose” an electron is called ionization energy
Anions
-
- Anions form when electrons are gained by an atom
- Non-metals form anions
- The energy released with the electron is called electron affinity
Isoelectronic
When atoms form ions, they often have a “noble gas-like” arrangement and atoms/ions end up with the same number of electrons. This is called isoelectronic.
Isotopes
- A form of an element in which the atoms have the same number of protons but a different number of neutrons. So they have different masses
- You can determine the isotopic abundance of a sample using a mass spectrometer.
Radioactive Decay
Radioactive Decay is the spontaneous disintegration of an unstable isotope
Nuclear Radiation
Nuclear Radiation is energy or small particles emitted from a radioisotope as it decays
Radioisotopes
Radioisotopes is an isotope that spontaneously decays to produce 2 or more smaller nuclei and radiation
Radioactive
Radioactive means that a substance has the potential to emit nuclear radiation on decay
Types of Radiation
Alpha Particle - a positive charged particle with the same structure as the helium particle
Beta Particle - a negative charged particle that is identical to an electron
Gamma Ray - a form of high-energy particle electromagnetic radiation emitted by some radioisotopes
Equations
Check document
Determining Atomic Mass of Elements
Atomic mass = (% abundance of isotope 1 x mass of isotope 1) + (% abundance of isotope 2 x mass of isotope 2) / 100
Groups
- Elements show similar chemical properties
- Elements show similar trends in their chemical properties
Periods
- As you move across periods, changes in the chemical and physical properties that are repeated in the next period
- This is what “period” and “periodic” refers to
Physical Properties
Identify and explain the trends in the physical properties of the first 20 elements including: Atomic radius Ionic radius First ionization energy Electronegativity Melting point
Atomic Radius
- This is the size of the atom
- There is no simple measure as atoms do not have a well defined “edge”
- We use the: covalent radius
- This is half the distance between the nuclei of two atoms in a covalent bond
- This means we do not have values for the noble gases as they do not form bonds
- The main factors influencing atomic radius are:
- Number of shells (the principal quantum number)
- The charge of the nucleus
Periodic Trends - Atomic Radius
- Bottom-left - large atomic radius
- Top-right - small atomic radius
Ionic Radius
- This is the “size” of an ion and is measured in a similar way to atomic radius
- The main factors influencing ionic radius are:
- Number of shells (the principal quantum number)… don’t forget this can be affected by the type of ion formed
- The charge of the nucleus
Periodic Trends - Ionic Radius
- Positive ions
- Smaller than the ion they are derived from (Na bigger than Na+)
- Isoelectronic positive ions
- More protons, smaller radius, pull in electrons
- Negative ions
- Bigger than the ion they are derived from (Cl smaller than Cl-)
- Isoelectronic negative ions
- More protons, smaller radius, pulls in electrons
First Ionization Energy
- This is the energy required to remove one mole of electrons from one mole of gaseous atoms to form positive ions
- Ex: Ag (g) → Ag+ (g) + e-
- Values are positive because this is an endothermic process
- Values are influenced by:
- Number of inner electron shells (and their shielding)
- Charge on the nucleus
Periodic Trends - First Ionization Energy
- Lower ionization energy in lower left corner
- Higher ionization energy in upper right corner
Electron Affinity
- Define as the enthalpy change when an electron is added to an isolated atom in the gaseous state
- Ex: X (g) +e- → X- (g) measured in KJ mol-1
Periodic Trends - Electron Affinity
- Lower electron affinity in lower left corner
- Higher electron affinity in upper right corner