MCAT Atomic Theory and Composition Flashcards
What is matter?
Pure substances of a mixture.
Elements v. Compounds
Elements cannot be broken down into smaller parts whereas compounds can be broken down into constituent parts and has distinct chemical properties.
Atoms makes up elements and gives the distinct properties of that element.
Describe the components of atoms?
Neutrons - located in nucleus, contains a neutral ( no) charge.
Protons- located in nucleus, contains a positive charge.
Electrons - located in orbitals surrounding the nucleus, contains a negative charge.
Homogenous v. Heterogenous mixtures
Heterogenous - substances are different from each other.
Homogenous - substances are the same.
Atomic number v. Atomic mass
Atomic number represents that number of protons ( and the number of electrons if the atom neutral).
Atomic mass represents that number protons and neutrons and represents the mass of the atom.
Therefore we can find the number of neutrons by subtracting the atomic mass and atomic number.
Ions
When atoms contains unequal number of electrons.
Cations - lose electrons and has a + charge.
Anions - gain electrons and has a - charge.
Isotopes
Elements that has different number of neutrons, even though they contain different number of neutrons they have the same elemental identity.
Isotopes has the same chemical identity but different physical identity.
How do we measure the mass of isotopes
Via the atomic mass unit ( amu) which is the mass of of 1/12 of a carbon-12 atom.
The atomic mass ( or atomic weight) is the average weight of all of that element’s isotopes.
What’s the basis behind radioactive decay?
When the balancing forces between nucleons and electrons falls apart the nucleus can eject high energy particles or rays in an effort to establish equilibrium.
Alpha decay
Characterized with the ejection of an alpha particle.
4
2 He
- Alpha particle consists of 2 protons and 2 neutrons.
- We can a resulting atom with an atomic number that’s 4 less and an atomic number that’s 2 less.
Electron emission ( beta minus decay)
When a neutron is converted to a proton and an electron is expelled. This results in no change in the atomic mass but an increase in the atomic number.
Positron emission
Happens when a proton is converted to a neutron and a positron is emitted, results in a decrease in the atomic number but not the atomic mass.
Electron capture
Happens when a proton and electron are combined and turns into a neutron but no particles are released. This results in a decrease in atomic number but no change in atomic mass.
Gamma decay
A high energy gamma ray ( photon) is released, no change in atomic mass or atomic number.
How do we determine the half- life from a radioactive decay plot?
We identify the original amount at the top of the graph and see how long it takes for that amount to decrease by half.
Bohr model
Model that shows a proton with a single electron orbiting the proton in a single orbit.
The electrons in the orbit in discrete energy levels ( no in-between).
Energy levels of electrons further from the nucleus v. closer to the nucleus
Electrons further out from the nucleus has more energy than electrons closer to the nucleus.
What happens when electrons gain energy? When it loses energy?
When an electron moves to a higher energy orbital it gains energy from light ( photons) or heat.
When an electron moves from a higher energy orbital to a lower orbital it loses energy in form of light ( photons).
The energy released or absorbed is proportional to the difference in the energy of orbitals.
Electromagnetic radiation
Has waves and particle properties.
The energy is directionally proportional to the frequency. But frequency is the inverse of the wavelength.
Emission line spectrum v. Absorption line spectrum
Electrons are absorbed or emitted in specific energies creating line spectrums.
Excited state v. Ground state
Excited state is when an electron gains energy and move up to a higher energy orbital.
Ground state is when an electron releases energy and moves to a lower energy orbital.
Heisenberg uncertainty principle
Principle that states we cannot determine both the momentum and the position with accuracy. The more we know of one variable the less we know of the other.
Quantum numbers
Acts like an address in identifying the general area of where an electron orbit.
- Principal quantum number ( n) - the main energy level.(1,2,3,4,5,6,etc)
- Angular quantum number (l)- the number of subshells within the main shell. ( 0(s),1(p),2(d),3(f),4(g),5 (h) etc..)
- Magnetic quantum number ( ml) - represents the number of orbitals within the subshell. ( 1,3,5,7,9). Each orbital in a subshell holds 2 electrons.
- Electron spin number (ms)- represents the spin of the electron, +1/2 or -1/2.
Pauli exclusion principle
No 2 electrons has the same set of 4 quantum numbers. In an orbital they have opposite spins since everything is equal.
Electron configuration
Sequence that describes the placement of electrons in shells and subshells.
We can determine this from the periodic table. The exceptions to the traditional patterns is chromium and copper.
Aufbau principle
States that electrons are filled into the lowest energy orbitals first and then the highest.
Hund’s rule
Electrons are placed singly in each orbital first and then we double back to pair the electrons.
How to find half- life?
1/2^ # of half lives
Valence electrons and core electrons
Valence electrons are the outermost electrons and influences the properties of atoms. Because of this atoms in the same group has the same chemical properties.
Core electrons are in-between the nucleus and valence electrons and partially blocks the electrostatic attraction between the nucleus and valence electrons.
Noble gas configuration
A short hand notation where we start at the latest noble gas and start the configuration from there.
How does the electron configurations of ions change?
With anions we add electrons to the lowest energy unfilled orbital first.
With cations we remove electrons from the highest principle energy level.
Paramagnetic atoms v. Diamagnetic atoms
Paramagnetic atoms has unpaired electrons in their orbitals and is attracted to external magnetic fields.
Diamagnetic atoms has paired electrons that are not attracted to an external magnetic field.
How is the periodic table organized?
Increasing atomic mass in horizontal rows called periods.
Vertical rows are called groups or families and contains the same number of valence electrons, this causes them to have the same chemical properties.
What does roman numerals represent on top of each group of the periodic table?
The number of valence electrons.
Where are the following groups located on the periodic table?
Metals, nonmetals, and metalloids.
Metals are to the left of the periodic table, nonmetals to the right of the periodic table, metalloids are along the stairstep line.
What are the properties of metals, nonmetals, and metalloids?
Metals - good conductors of heat and electricity.
Nonmetals - brittle, dull, poor conductors of heat and electricity.
Metalloids- Has properties in-between metals and nonmetals.
Main groups elements v. Transition elements
Main group elements are in groups 1-2 and 13-18. Valence electrons are in the s and p blocks.
Transition elements are in 3-12. Their electrons are located in d block.
Diatomic elements
Elements in the halogen groups that naturally exist as 2 elements.
Alkali metals ( group 1 metals)
highly reactive and readily donate electrons (metal properties) , forms +1 charge.
Alkali earth models ( group 2 metals)
similar to alkali metals, readily forms +2 charge.
Transition metals
They can lose difference valence electrons forming different ions of the same element.
Chalcogens
Group 16, readily accepts 2 electrons for from -2 anion.
Halogens
Group 17, readily accepts 1 electron to form -1 anion.
Noble gases
Group 18, inert gases because they have the desired octet.
What is Zeff ( effective nuclear charge) and how do we calculate it?
Zeff is the attraction that the nucleus has for valence electrons.
Zeff = Z ( nuclear charge) - S (shielding constant)
The shielding constant represents the shielding between the nucleus and electrons.
Determine the Z by determining the charge of the protons. S is determined by finding the number of core electrons.
Atomic radius
The distance between the nucleus and valence electrons.
Decrease from bottpm to top and from left to right.
Electronegativity
The pull force for electrons in a covalent bond.
Increases from bottom to top and left to right.
Atoms with a larger Zeff and therefore a smaller radius has smaller electronegativities.
Electron affinity
How readily an atom accepts an electron.
Exothermic reaction. The more strongly the atom holds onto valence electrons the greater the electron affinity.
Ionization energy
Energy required remove an electron.
Group 1 has the lowest ionization energies while group 18 has the highest ionization energies.
Atoms with greater Zeff, smaller radii has a greater ionization energy.
Each subsequent ionization energy is greater because the Zeff increases with each electron removed.
Dalton’s atomic theory
Law that states the atoms of the SAME element has the same shape and mass.
What are multivalent ions?
Ions that have a charge greater than 1 (can be negative, just the number itself has to be greater than one).
What are the diatomic molecules?
N, O, F, Cl, Br, I
Oxygen has a Lewis diagram with double bonds
Nitrogen has a Lewis diagram with triple bonds.
All other of the diatomic molecules has a single bond.
Empirical v. Molecular formula. How to find empirical formula?
Empirical formula is the formula in its most simplified ratios.
Molecular formula is the formular that represents actual number of atoms.
To find empirical formula divide the mass given to you by the molar mass of the atom (from the periodic table) you then divide each ratio by the smallest calculated ratio.
Remember, the molar mass must equal to the calculated empirical formula mass so if it doesn’t you have to multiple each ratio so that it will equal the given molar mass.
Electronic v. Molecular geometry
Electronic geometry describes atom shape in terms of bonding and nonbonding electrons.
Molecular biology describes the atom shape in terms of bonding electrons.
Describe the molecular VESPR shapes
2- linear (180 degrees)
3- trigonal planar (120 degrees)
4- tetrahedral (109.5 degrees)
5- trigonal bipyramidal (90 degrees)
6- Octahedral (90 degrees)
