Chapter 3: Atoms, Elements, and the Building Blocks of Matter Flashcards
2 and 3
2: atomic number, number of protons, also same as the number of electrons surrounding the nucleus of an element in its neutral state.
3: The molar mass of the element. It’s also called the atomic weight
Mass number and isotopes
Mass number: sum of neutros and protons
Isotope: different numbers of neutrons. Example - carbon-12 contains 6 protons and 6 neturons, and carbon-14 contains 6 protons and 8 neutrons. These are isotopes of carbon
Molar mass on periodic table - average of all the mass numbers of all known isotopes
What are the horizontal and vertical rows called on the periodic table?
Periods: horizontal rows
Groups: verticle columns
What do the coefficients in chemical reactions tell you?
About the reactants and products in terms of moles
Avagadro’s number
1 mole = 6.022 x 1023 molecules
Moles = Molecules/(6.022 x 1023)
What are the atomic weights on the periodic table?
They are given in terms of atomic mass units (amu), but an amu is the same as a gram per mole, so if 1 carbon weighs 12 amu, then 1 mol of carbon atoms weighs 12 grams.
Equation to convert between grams & moles
Moles = grams/molar mass
What is the ideal gas equation?
PV = nRT
P = pressure
V = Volume (L)
T = Temperature (K)
R = the gas constant, 0.0821 L-atm/mol-K
What is STP?
Where P = 1 atm
T = 273
And, in this situation, one mole of gas always occupies 22.4 L
So Moles = liters/(22.4 L/mol)
Other ways for finding Moles =
(molarity)(liters of solution)
(molality)(kilograms of solvent)
What is percent composition (or mass percent)?
Percent by mass of each element that makes up a compound
Calculated by dividing the mass of each element or component in a compound / by the total molar mass for the substance (x 100%)
Emperical Formula
Molecular Formula
Represents the simplest ration of one element to another in a compound. Example: CH2O
Represents the actual formula for the substance. Example: C6H12O6
What are quantum numbers?
Numbers that describe the positions of the electrons in relation to the nucleus
Each electron has 4 ________ that apply to its **shell, subshell, oribtal, **and spin.
Shells
n =1, 2, 3…
In a hydrogen atom, the principal quantum number, or shell, of an electron determines its averge distance from the nucleus as well as its energy.
So, electrons in shells with higher values are farther away on average from the nucleus and will have more energy and less stability than electrons in shells with lower values.
Subshells
L = 0, 1, 2…
The angular momentum quantum number, or subshell, describes the shape of an electron’s orbital
- First shell (n = 1) has 1 subshell: s, or l = 0 [n - 1]
- Second shell (n = 2) has 2 subshells: s (l = 0) and p (l = 1)
- Third shell (n = 3) has 3 subshells: s (l = 0), p (l = 1), & d (l = 2)
Orbitals of s sbushells are spherical
Oritals of p subshells are dumbbell shaped
Orbitals
ml, = … -1, 0, +1...
The magnetic quantum number, or orbital, describes the orientation of the orbital in space
Describes whether the path of the electron lies mostlhy on the x, y, or z axis of a 3-dimensional grid
- s subshell (l = 0) has 1 orbital: ml = 0
- p subshell (l = 1) has 3 orbitals: ml = -1, m<em>l</em> = 0, ml = +1
- d subshell (l = 2) has 5 orbitals: m<em>l</em> = -2, -1, 0, 1, and 2
Spin
ms = +1/2, -1/2
Each orbital can contain 2 electrons: one with a positive spin and one with a negative spin
Aufbau Principle
When building up the electron configuration of an atom, electrons are placed in orbitals, subshells, ad shells in order of increasing energy
Pauli Exclusion Principle
Within an atom no electron can have the same set off quantum numbers. Each electron in any atom has its own distinct set of 4 quantum numbers
Hund’s Rule
When an electron is added to a subshell, it will always occupy an empty oribtal if one is availabe. Electrons always occupy orbitals singly if possible and pairup if no empty orbitals are available
Electrons and Energy
Electrons have potential energy that increases with their distance from the nucleus
Energy of electrons is quantized. Means that electrons can exist only at specific energy levels, separated by specific intervals. Ex. - brick in the building could be placed only on 1st, 2nd, or 3rd floor, but not in between
Quantized energy of an electron in an H atom can be found if you know its principal quantum number or shell
How do you find the energy of an electron?
E<em>n</em> = -2.178 x 10-8/n2 Joules
E<em>n</em>= energy of the electron
<em>n</em> = principal quantum number of the electron
What happens when atoms absorb energy in the form of electromagnetic radiation?
Electrons jump to higher energy levels. When electrons drop from higher to lower energy levels, atoms give off energy in the form of electromagnetic radiation.
Relationship between the change in energy level of an electron and the electromagnetic radiation absorbed or emitted
Energy and Electromagnetic Radiation
ΔE = hv = hc/λ
ΔE = energy change
- h *= Planck’s constant, 6.63 x 10-34 joule-sec
- v* = frequency of the radiation
λ = wavelength of the radiation
c = the speed of light, 3.00 x 108 m/sec (c = λf)
energy level changes for the electrons of a particular atom are always the same, so atoms can be identified by their emission & absorption spectra
Dalton’s Elements
John Dalton:
- There are many different kinds of atoms, called elements
- These elements combine to form compounds - always contain the same ratios of elements. Ex. - Water (H2O) always has 2 hydrogen atoms for every oxygen atom
- Atoms are never created or destroyed in chemical reactions
Development of the Periodic Table
Dmitri Mendeleev and Lothar Meyer
Thomson’s Experiment
J.J Thomson watched the deflection of charges in a cathode ray tube and said that atoms are composed of positve and negative charges. The negative charges were called electrons sprinkled throughout the positively charged atom like chocolate chips sprinkled through a blob of cookie dough.
Millikan’s Experiment
Calculated the charge on an electron by examining the behavior of charged oil drops in an electric field
Plum Pudding Model
Rutherford’s Experiment
Ernest Rutherford fired alpha particles at gold foil & observed how they were scattered. Led him to conclude that all positive charge in an atom was concentrated at the center and that an atom is mostly empty space. Led to the ide athat an ato has a positively charged nucleus, which contains most of the atom’s mass, and that the tiny negatively charged electrosn travel around the nucleus.
Quantum Theory
Max Planck figured out that electromagnetic energy is quantized. That is, for a given frequency of radiation (or light), all possible energies are multiples of a certain unit of energy, called a quantum (mathematically, thats E = hv).
Bohr Model
Neils Bohr predicted that electrons orbit the nucleus at specific, fixed radii. Bohr model worked for atoms and ions with one electron but not for more complex atoms.
Heisenberg Uncertainty Principle
Werner Heisenberg: impossible to know bot the position and momentum of an electron at a particular instant. An electron orbital is a probability function
De Broglie Hypothesis
All matter has wave characeristics. Sometimes the behavior of electrons is better described in terms of waves than particles
De Broglie equation
De Broglie’s hypthesis is useful for very small particles, such as electrons. For larger particles, the wavelength becomes too small to be of interest
Periodic trends
The closer the electron is ot he nucleus, the more stronger it is attracted
The more protons in a nucleus, the more strongly an electron is attracted
Electrons are repelled by other electrons in an atom. So if other electrons are between a valence electron and the nucleus, the valence electron will be less attracted to the nucleus. That’s called sheilding
Completed shells (and to a lesser extent, completed subshells) are very stable. Atoms prefer to add or subtract valence electrons to create complete shells if possible.
Metallic character of the elements decreases as you move from left to right across the periodic table. The elements in the borderline between metal and nonmental, such as silicon and arsenic, are called metalloids.
Atomic Radius
The approximate distance from the nucleus of an atom to its valence electrons
Moving from left to right across a period
Atomic radius decreases
(Li - Ne for example)
Moving from left to right, protons are added to the nucleus. Electrons are also being added, but they are all in the same shell at about the same distance from the nucleus, so there is not much of a sheilding effect.
Moving Down a Group
(Li to Cs, for instance) Atomic Radius increases
Moving down a group, shells of eectrons are added to the nucleus. Each shell shields the more distant shells from the nucleus and the valence electrons get farther away from the nucleus. Protons are also being added, but the shielding effect of the negatively charged electron shells cancels out the positive charge.
Cations
Smaller than atoms
When an electron is removed from an atom, the outer shell is lost, making the cation smaller than the atom. Also, when electrons are removed, electron-electron repulstions are reduced, allowing all of the remaining valence electrons to move close to the nucleus.
Anions
Negatively charged Ions
Larger than Atoms
When an electron is added to an atom, forming an anion, electron-electron repulsions increase, causing the valence electrons to move farther apart, which increases the radius
Ionization energy
Electrons are attracted to the nucleus of an atom, so it takes enrgy to remove an electron. The energy required to remove an electron from an atom is called the first ionization energy. Once it has been removed, the atom becomes a positively charged ion. The energy required to remove the next electron from the ion is called the second ionization energy, etc.
Moving from left to right acrss a period…
Ionization energy increases
Protons are added to the nucleus, which increases its positive charge. for this reason, the valence electrons are more strongly attracted o the nucleus, which increases the energy required to move them. Electrons are also being added, but sheilding effect provided by the filling of the s subshell causes slight deviation in the trend in moving from Group 2A to Group 3A
There is also a slight deviation when the electrons in the p subshell start to pair up, so oxygen has a slightly lower first ionization energy than nitrogen does.
Moving Down a Group
Ionization Energy Decreases
Shells of electrons are added to the nucleus
Inner shell shields the more distant shells from the nucleus, reducing the pull of the nucleus on the valence electrons and making them easier to remove
Protons also being added, but sheilding effect cancels
Second Ionization Energy
Greater than the First because when an electron has been removed from an atom, electron-electron repulsion decreases and the remaining valence electrons move closer to the nucelus. This increases the attractive force
Electron affinity
A measure of the change in energy of an atom when an electron is added to it
When the addition of an electron makes the atom more stable, energy is given off
When the addition of an electron makes the atom less stable, energy must be placed in a higher energy level, making the element less stable.
Electronegativity
Refers to how strongly the nucleus of an atom attracts the electrons of other atoms in a bond.
Electronnegativities of elements are estimated based on ionization energies and electron affinities, and they basically follow the same trends.
Moving from left to right across a period, electronegativity increases
Moving down a goup, electronnegativity decreases
