MCAT Atomic Theory and Composition

Question 1

What is matter?

Answer 1

Pure substances of a mixture.

Question 2

Elements v. Compounds

Answer 2

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.

Question 3

Describe the components of atoms?

Answer 3

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.

Question 4

Homogenous v. Heterogenous mixtures

Answer 4

Heterogenous - substances are different from each other.

Homogenous - substances are the same.

Question 5

Atomic number v. Atomic mass

Answer 5

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.

Question 6

Ions

Answer 6

When atoms contains unequal number of electrons.

Cations - lose electrons and has a + charge.

Anions - gain electrons and has a - charge.

Question 7

Isotopes

Answer 7

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.

Question 8

How do we measure the mass of isotopes

Answer 8

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.

Question 9

What’s the basis behind radioactive decay?

Answer 9

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.

Question 10

Alpha decay

Answer 10

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.

Question 11

Electron emission ( beta minus decay)

Answer 11

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.

Question 12

Positron emission

Answer 12

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.

Question 13

Electron capture

Answer 13

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.

Question 14

Gamma decay

Answer 14

A high energy gamma ray ( photon) is released, no change in atomic mass or atomic number.

Question 15

How do we determine the half- life from a radioactive decay plot?

Answer 15

We identify the original amount at the top of the graph and see how long it takes for that amount to decrease by half.

Question 16

Bohr model

Answer 16

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).

Question 17

Energy levels of electrons further from the nucleus v. closer to the nucleus

Answer 17

Electrons further out from the nucleus has more energy than electrons closer to the nucleus.

Question 18

What happens when electrons gain energy? When it loses energy?

Answer 18

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.

Question 19

Electromagnetic radiation

Answer 19

Has waves and particle properties.

The energy is directionally proportional to the frequency. But frequency is the inverse of the wavelength.

Question 20

Emission line spectrum v. Absorption line spectrum

Answer 20

Electrons are absorbed or emitted in specific energies creating line spectrums.

Question 21

Excited state v. Ground state

Answer 21

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.

Question 22

Heisenberg uncertainty principle

Answer 22

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.

Question 23

Quantum numbers

Answer 23

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.

Question 24

Pauli exclusion principle

Answer 24

No 2 electrons has the same set of 4 quantum numbers. In an orbital they have opposite spins since everything is equal.

Question 25

Electron configuration

Answer 25

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.

Question 26

Aufbau principle

Answer 26

States that electrons are filled into the lowest energy orbitals first and then the highest.

Question 27

Hund’s rule

Answer 27

Electrons are placed singly in each orbital first and then we double back to pair the electrons.

Question 28

How to find half- life?

Answer 28

1/2^ # of half lives

Question 29

Valence electrons and core electrons

Answer 29

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.

Question 30

Noble gas configuration

Answer 30

A short hand notation where we start at the latest noble gas and start the configuration from there.

Question 31

How does the electron configurations of ions change?

Answer 31

With anions we add electrons to the lowest energy unfilled orbital first.

With cations we remove electrons from the highest principle energy level.

Question 32

Paramagnetic atoms v. Diamagnetic atoms

Answer 32

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.

Question 33

How is the periodic table organized?

Answer 33

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.

Question 34

What does roman numerals represent on top of each group of the periodic table?

Answer 34

The number of valence electrons.

Question 35

Where are the following groups located on the periodic table?
Metals, nonmetals, and metalloids.

Answer 35

Metals are to the left of the periodic table, nonmetals to the right of the periodic table, metalloids are along the stairstep line.

Question 36

What are the properties of metals, nonmetals, and metalloids?

Answer 36

Metals - good conductors of heat and electricity.

Nonmetals - brittle, dull, poor conductors of heat and electricity.

Metalloids- Has properties in-between metals and nonmetals.

Question 37

Main groups elements v. Transition elements

Answer 37

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.

Question 38

Diatomic elements

Answer 38

Elements in the halogen groups that naturally exist as 2 elements.

Question 39

Alkali metals ( group 1 metals)

Answer 39

highly reactive and readily donate electrons (metal properties) , forms +1 charge.

Question 40

Alkali earth models ( group 2 metals)

Answer 40

similar to alkali metals, readily forms +2 charge.

Question 41

Transition metals

Answer 41

They can lose difference valence electrons forming different ions of the same element.

Question 42

Chalcogens

Answer 42

Group 16, readily accepts 2 electrons for from -2 anion.

Question 43

Halogens

Answer 43

Group 17, readily accepts 1 electron to form -1 anion.

Question 44

Noble gases

Answer 44

Group 18, inert gases because they have the desired octet.

Question 45

What is Zeff ( effective nuclear charge) and how do we calculate it?

Answer 45

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.

Question 46

Atomic radius

Answer 46

The distance between the nucleus and valence electrons.

Decrease from bottpm to top and from left to right.

Question 47

Electronegativity

Answer 47

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.

Question 48

Electron affinity

Answer 48

How readily an atom accepts an electron.

Exothermic reaction. The more strongly the atom holds onto valence electrons the greater the electron affinity.

Question 49

Ionization energy

Answer 49

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.

Question 50

Dalton’s atomic theory

Answer 50

Law that states the atoms of the SAME element has the same shape and mass.

Question 51

What are multivalent ions?

Answer 51

Ions that have a charge greater than 1 (can be negative, just the number itself has to be greater than one).

Question 52

What are the diatomic molecules?

Answer 52

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.

Question 53

Empirical v. Molecular formula. How to find empirical formula?

Answer 53

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.

Question 54

Electronic v. Molecular geometry

Answer 54

Electronic geometry describes atom shape in terms of bonding and nonbonding electrons.

Molecular biology describes the atom shape in terms of bonding electrons.

Question 55

Describe the molecular VESPR shapes

Answer 55

2- linear (180 degrees)
3- trigonal planar (120 degrees)
4- tetrahedral (109.5 degrees)
5- trigonal bipyramidal (90 degrees)
6- Octahedral (90 degrees)