Unit 1 - Matter, Chemical Trends and Bonding Flashcards
What is empirical knowledge?
knowledge that comes from investigation and observation
What is theoretical knowledge?
applying knowledge to explain scientific observations
What is an atom?
- the smallest unit of an element that can be divided and still be that element
Example: The smallest particle of carbon is a single atom of carbon. If you divide it is no longer carbon anymore
Atomic Theory - Democritus + what did he propose?
theorized that matter is composed of tiny, indivisible particles called atomos
Proposed:
-Atoms are small hard particles.
-Made of a single material that’s formed into different shapes and sizes
- They are always moving
- They form different materials by joining together.
Atomic Theory - Dalton + what did he propose?
- Elements are composed of small, indivisible particles called atoms and that each unique element is composed of a single type of atom
- Atoms of one element are different from the atoms of all other elements
- During chemical reactions, atoms are combined, separated, or rearranged into different ratios
Atomic Theory - JJ Thompson + what did he propose?
- Performed experiments with cathode ray tubes
- When charged electric plates are placed around the cathode ray, the beam veered away from the
negatively charged plate - By measuring the deflection of the rays, he was able to determine that the particle was two thousand times lighter than a hydrogen atom
CONCLUSION:
- a sub-atomic particle exists
- this sub-atomic particle is negatively charged (ELECTRON)
What is the Thompson model?
- Plum pudding
- First model to confirm that atoms are made up of smaller subatomic particles
Knew that atoms were neutral, so a positively-charged particle must also exist
Atomic Theory - Rutherford + what did he propose?
- Performed the gold foil experiment (Shot positively charged alpha particles (He2+) through a thin sheet of gold and based on Thomson’s model, most of the particles should have gone straight through)
- While most alpha particles went through the foil, some were deflected at large angles
- Rutherford theorized that the alpha particles were hitting something dense and positively-charged
What is the Rutherford model?
The planetary model
- Proposed that the positively charge of an atom was concentrated in the centre of an atom
- Electrons orbits the nucleus like planets
Issues of the Rutherford model?
- nucleus composed only of positive charge should break apart due to electrostatic repulsion
- The positively-charged particles could not account for the total mass of the atom
Atomic Theory - Bohr + what did he propose?
- observed that the hydrogen atoms emitted
light of only certain colours when they were
”excited”
What is the Bohr model?
- Electrons orbit the nucleus of the atom in definite energy levels
- Electrons can “jump” between orbits by absorbing or emitting photons carrying an amount of energy that is equal to the difference in the energy levels of the electrons
What is an isotope?
Atoms of an element with the same # of protons but different # of neutrons
What is isotopic abundance?
The % of an isotope in a sample of an element
What is atomic mass?
The atoms average weight from the isotopes
What is a mass spectrometer?
Used to identify isotopes and their relative abundance
1. Vaporization
2. Ionization
3. Acceleration
4. Deflection
5. Detection
What is nuclear radiation?
- When some isotopes are unstable and radioactively decay
- Some isotopes decay and emit radiation
a) Alpha particles (a) -has the same nuclear structure as He-4
b) Beta particle (β) - Negatively charged electron
c) Gamma Ray (γ) - Is a form of high-energy electromagnetic radiation
What are valence electrons and core electrons?
- Electrons found in the outermost shell
- Electrons that aren’t valence electrons (inside)
What is atomic radius and its trend?
Defined as the distance from the nucleus to the valence electrons
Trend:
- As you go down it increases
- As you move left to right, it decreases
What is a nuclear charge?
The charge of the nucleus
- Core electrons can reduce the positive nuclear charge –> shielding by the outer electrons (to not add anymore electrons –> keep neutral)
What is an ionic radius?
When cations form, the number of electron orbits decreases. Each remaining electron feels a stronger attraction to the nucleus
- When anions form, there is more electron-electron repulsion Zeff is ”shared” among more electrons
What is electron affinity?
The amount of energy needed to gain an electron
What is electronegativity?
The atoms ability to attract electrons
What is ionization?
How much energy it takes for an atom to lose an electron
What is the structure of ionic compounds?
They form a crystal lattice structure
- The smallest repeating unit is called a formula unit
What are the properties of ionic compounds?
- High melting and boiling point
- Solid at room temp –> strong electrostatic forces
- Many are soluble in water
- Conduct electricity well
- Hard but brittle
ex. When you hit a hammer on it, the structure changes and cause the like charges to repel and break
What are the properties of molecular substances?
- Exist as gases, liquids, and solids at room temp
- Low boiling points and melting points
- Poor conductors of electricity
- Do not dissolve in water
What is covalent bonding?
When a pair of electrons are shared by 2 atoms + molecular
How to tell if something is ionic or molecular?
Calculate the electronegativity difference between 2 elements
What are non-polar bonds?
Equal sharing of electrons
What are polar bonds?
Unequal sharing of electrons (positive and negative charges)
- Have charged ends
What is intramolecular forces?
Within a molecule (ionic and covalent bonds)
What are intermolecular forces?
Forces of attraction between molecules which determine the physical properties (stronger intermolecular forces = stronger physical properties) (dipole dipole, london, hydrogen)
What is dipole-dipole forces?
Negatively charged ends attract to the positively charged end
- Permanent
- Polar bonds
What is london dispersion forces?
When a negative and positively charge create a temporary charge accidentally
What is hydrogen bonding?
When hydrogen atoms bonds with N, O, F
Why is water dense?
- The solid state of most compounds is more dense than the liquid state, so the solid therefore sinks in the liquid
- Ice, however, is less dense than liquid water so it floats in liquid water
- This is because the hydrogen bonds in water arrange the molecules in a crystalline structure, leaving gaps between molecules
What causes surface tension?
- caused by the forces of attraction between molecules at the surface of the liquid
What is viscosity?
In general, the stronger the intermolecular forces, the higher the viscosity of the liquid
- describes a liquid’s resistance to flow
What is the pattern of solubility?
- Polar substances tend to dissolve well in polar solvents, while non-polar substances tend to dissolve well in non-polar substances (like dissolves like)
- Due to water’s polarity, when ionic or polar substances are added to water, new intermolecular forces are formed between water molecules and the solute
