Chem. Unit 2
Who were the three scientists who contributed to the development of the periodic table?
1. German Chemist J.W. Dobereiner 2. English scientist John Newlands 3. Russian chemist Dimitri Mendeleev
Alkali Metals:
-Group 1A -Very reactive -Good conductors -Malleable -Ductile -One loosely bound valence electron -Can explode when exposed to water -They want to dump off an electron to become a positive ion, cation.
Halogens:
-Group 17 or 7A -Extermely reactive gases that form anions, ions with one negative charge -Very high electronegatives -Seven valence electrons -Highly reactive with alkaline earth and alkali metals
Noble Gases:
-Group 18 or 8A -Fairly nonreactive -Complete valence shell -Very low electronegativities -Low boiling points -All gases at room temperature
Electron Affinity of an element depends on:
1. Extent of nuclear charge 2. Size of the atom 3. Stability of valence shell (electron configuration)
Modern Periodic table:
-118 elements -18 groups -7 periods -Arranged by atomic number -A predictive model based on the arrangements of electrons in the elements.
Main Group Elements:
-Also called representative elements, are elements in Groups 1, 2, and 13-18. -They display a wide range of physical and chemical properties. -In their atoms, the s and p sublevels in the highest occupied energy levels are partially filled.
Anions:
-Anions have a negative charge of 1- -Non-metals tend to gain electrons to become monatomic ions. EX: when flourine gains an electron, it becomes a flourine ion, which has 1- charge. -Anions are bigger than their parent ions
Cations:
-Cations have a positive charge of 1+ -Metals tend to lose electrons to become cations. EX: when sodium loses one electron, it becomes a sodium ion, which has 1+ charge. -Cations are smaller than their parent ions -The charge of a cation depends on the number of valence electrons that have been lost.
Metals:
-Elements that are good conductors of heat and electrical current. -They are solid at room temperature -80% of elements are metals -Most are malleable -Many are ductile
Non-metals:
-Elements that tend to be a poor conductor of heat and electrical current. -Brittle -They have opposite properties of metals -Except carbon as graphite is a good conductor of electric current.
Metalloids:
-Elements that tend to have similar properties of metals and non-metals. -All solids -Poor conductors of heat and electricity -Can be changed by using mixtures (ex: pure silicon is a poor conductor of electricity but when mixed with boron, it produces a good electrical conductor). -They can manipulate conductivity -They don't exhibit luster -Can become semi conductors when mixed together
Alkaline Earth Metals:
-Group 2A -Low electron affinities and electronegatives -Two electrons in the outer shell -Smaller atomic radii than Alkali Metals -Readily form divalent cations (two charges instead of just one)
Atomic Radius in groups and periods:
-In groups the atomic radius becomes larger down a group because valence electrons occupy higher energy shells, which extend further away from the nucleus. -In periods, the atomic radius decreases across a period because the number of electrons and protons are changing. As more protons are added across a period, Zeff increases.
1869-1871 Mendeleev's Periodic Tables
-Mendeleev published his first periodic table in 1869 by observing patterns and combining known information, such as Dobereiner's triads and Newlands octaves. -In 1871, Mendeleev rearranged the 1869 table format that is similar to what they use today. He predicted the existence of undiscovered elements based on gaps in patterns of properties. He left spaces for these undiscovered elements in his periodic table. -Her arranged his periodic table in order of atomic mass.
Ionization energies:
-Metals have a low Zeff because they lose electrons when forming ions, and have a relatively low I1 (first ionization energy). -Non-metals have a higher Zeff because they gain electrons when forming ions, and have a higher I1 (first ionization level). -Noble gases have an even higher I1 because they experience a very high nuclear charge.
Shielding effect on core and valence electrons:
-Negatively charged electrons are attracted to a positively charged nucleus. -Core electrons experience a greater force of attraction to the nucleus than valence electrons. -Valence electrons are repelled by core electrons. This repulsion offsets some of the attraction of the valence electrons to the nucleus.
Atomic Radius:
-One-half the distance between the nuclei of the two atoms of the same elements. It is used to estimate the size of an atom. -Increases right to left (because there is more attraction force from left to right) and increases down a group (because more shells are being added). -Measured in picometers, pm.
Electron Affinity:
-The energy change that happens when an atom gains an electron (energy goes out and atoms goes in). -For most atoms, energy is released when an electron is added to the atom. An atom with a higher electron affinity will release a greater amount of energy. A higher electron affinity has a more negative electron affinity value. -Increases left to right and decreases top to bottom.
Ionization Energy:
-The energy required to remove the outermost electron from the ground state of the gaseous atom. -Increases left to right and increases top to bottom -The size of an atom directly affects its ionization energy. Coulumb's Law states that the closer an electron is to the nucleus, the stronger the force of attraction, and therefore the more energy required to remove the electron. -Small atoms tend to have high ionization energy and large atoms have lower ionization energies. -Ionization increase and decrease are opposite of the increase and decrease of atomic radii.
F=K q₁*q₂/r²
-The force (F) is directly proportional to charge, q. The larger the absolute value of the charge carried by each particle, the greater is the force between them. -the force is inversely proportional to the square of the distance (d) between the two particles. The farther apart the particles are, the weaker is the force.
Effective Nuclear Charge, Zeff:
-The net positive nuclear charge experienced by an electron in an atom. The charge is usually not the full nuclear charge because of the shielding effect. -The effective nuclear charge can be calculated with this equation: Zeff= Z-S (Z is the atomic number and S is the number of shielding electrons-core electrons) -The effective nuclear charge increases left to right on the periodic table and decreases down a group.
Shielding Effect:
-The repulsive forces between electrons work to reduce how much of the attractive force each electron "feels." -The amount of shielding an electron experiences depends on which orbital the electron is in. Inner core electrons always shield valence electrons, but valence electrons don't shield one another.
Electron Configuration:
-The way electrons are arranged around the nucleus of an atom. An element's chemical and physical properties are due to the element's electron configuration. -You can use the periodic table to help determine an element's electron configuration and its properties. -Elements in the same group of the table have related outer shell configurations.
Periodic trend of electron affinity:
-This only applies to main group elements with the exception of group 18. -Increases left to right across a period and up a group.
Coulomb's Law with charges:
-Two oppositely charged particles attract. The particles have equal but opposite charges. -A larger charge produces a larger force of attraction. -A larger distance produces a smaller force of attraction.
A main group element has 81 protons and an estimated effective nuclear charge of +3. Therefore, the element has _____ core electrons and can be found in group ____ of the periodic table.
78, 3A
Which statements are true concerning elements in the same group in the periodic table? Select all that apply: A: They have similar periodic properties B: They are all metals or nonmetals, but not both C: They are either all solids or all liquids or all gases D: They have the same number of shells as electrons E: They have the same number of inner core electrons F: They have the same outer shell electron configuration
A: They have similar periodic properties F: They have the same outer shell electron configuration
Why are anions always bigger than their parent atoms?
Anions are always bigger than their parent ions because they're gaining electrons. Since the number of protons stay the same, there is a lower Zeff per electron, which allows the extra electrons move farther from the nucleus.
Lithium is in Group 1A, Period 2 of the periodic table. Which statement describes the charge of the ion it typically forms? A: It forms a cation with +2 charge B: It forms a cations with a +1 charge C: It forms an anion with a +1 charge D: It forms a anion with a -1 charge
B: It forms a cation with a +1 charge
Which of the following correctly completes the statement: Cations are always_____ than the parent atom and anions are always___ than the parent atom> A: Smaller, smaller B: Larger, smaller C: Smaller, larger D: Larger, larger
C: Smaller, larger
Why are cations always smaller than their parent atoms?
Cations are always smaller than their parent ions because they're losing an electron. When they lose electrons they loose energy shells, creating a smaller atomic radius.
1829 Dobereiner's Triads
Dobereiner arranged elements into groups of three, or triads. He noticed a pattern where the middle element of a triad tended to have properties that were midway between those of the other two elements.
How to determine what group element it is based off of it's ionization levels:
EX: Let's say the biggest jump in ionization energies is 3-4, the element has 3 valence electrons and is in group 3A. It has 3 valence electrons because going from one energy level down takes a lot of ionization enegry and it went from the third valence electron to the first core electron. The ionization energies always go one more than the valence electron.
Coulombs law:
F=K q₁*q₂/r², magnitude of force between two charges -Coulomb's law tells us that the strength of the force between two charged particles depends on the charge of each particle and the distance between them. -Helps us interpret how strongly the nucleus attracts different electrons in an atom.
Charges commonly formed for select nonmetals:
Group 17 nonmetals gain one electron to form anions with a 1- charge. Groups 15 and 16 form anions with 3- and 2- charges.
Period:
Horizontal row of elements in the periodic table.
Electron Affinity and Ionization Energy appear to be opposing concepts. Explain, using main group elements only, why they both share similar periodic trends in a period and column.
If it's harder to take, it's easier to give. The bigger the ionization energy, the easier it is to give and the harder it is to take an electron from the atom.
Periodic trend of ionization energy:
Increases moving left to right across a period and moving up a group.
Periodic trend of atomic radius:
Increases moving right to left across a period and down a group.
Based on their definitions, electron affinity could be considered the opposite of ____.
Ionization energy
The elements K, Ca, Se+, Kr, and Ga all appear in period 4 of the periodic table arrange them in order of their atomic size, from largest to smallest.
K, Ca, Ga, Se, Kr
Period Trend of a Metallic Character:
Metallic character increases moving diagonally across the periodic table from the upper right to the lower left corner. -Most metallic element is francium and the least in helium.
From which area on the periodic table are you most likely to find semiconductors?
Metalloids because when you mix metalloids together they become semi-conductors. Metalloids are able to manipulate conductivity allowing them to sometimes conduct electricity.
1865 Newlands' Octaves
Newlands organized the 56 elements by atomic weight. He published the law of octaves, proposing that every eighth element had similar properties to the first.
Periodic Trend of a Nonmetallic character:
Nonmetallic character increases moving diagonally across the periodic table from the lower left corner to the upper right corner. -Least nonmetallic is francium and most nonmetallic is helium.
The valence electrons of an atom do not experience the full attractive force of protons in the atom's nucleus due to the presence of the inner core electrons. The reduction in nuclear charge experienced by valence electrons due to the inner core electron is called the ___
Shielding effect
Periodic Law:
States that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
Charges commonly formed for select metals:
The charge of a cation depends on the number of valence electrons that have been lost. Group 1 metals lose one valence electron to form cations with 1+ charges. Group 2 metals lose two valence electrons to form cations with 2+ charges.
Core electrons:
The electrons that aren't valence electrons. To find the number of core electrons you subtract the number of valence electrons from the total amount of electrons in the atom.
Compare the trends for atomic size and first ionization level. Explain why these trends are related.
The smaller the atom, the larger the ionization energy required because the electrons are being held closer to the nucleus which means there is less distance and a greater force/ attraction to the nucleus.
Nonmetallic Character:
The tendency of an element to gain electrons and form anions.
Metallic Character:
The tendency of an element to lose electrons and form cations.
Why do noble gases have relatively low electron affinities?
They have low affinities because it's hard to add an electron to them because they don't want it.
Silicon and germanium are in the same group. How does the effective nuclear charge of silicon compare to that of germanium? Why is this the case?
They have the same effective nuclear charge because they have the same number of valence electrons. Silicon does, although, have a greater force because it has fewer shielding electrons.
Periodic trends:
Understanding periodic trends helps predict properties of elements based on their location in the periodic table.
Groups:
Vertical columns of element that have similar physical and chemical properties.
When asked why a chlorine atom gains one electron to form an anion with a 1- charge, a classmate answered "Because noble gas configurations are stable." Is this statement generally true?
Yes because atoms want to be as stable as they can be and that means for the electrons to fill up the lowest energy level as possible; that's exactly what noble gases do.
The effective nuclear charge, Zeff, experienced by valence electrons in an atom can be estimated from the equation: Zeff= the number of protons-the number of core electrons Using this estimation, effective nuclear charge for Main Group Elements would ______ to right across a period and __________ down a group.
increase, remain the same
