Chem 1305 exam 2

How do you draw an electron-dot structure? Where did these electrons come from? What are the pairs of electrons called in a dot structure? How many bonds will an element make?

1. Decide how many valence (outer shell) electrons are posessed by each atom in the molecule. 2. If there is more than one atom type in the molecule, put the most metallic or least electronegative atom in the center. Recall that electronegativity decreases as atom moves further away from fluorine on the periodic chart. 3. Arrange the electrons so that each atom contributes one electron to a single bond between each atom. 4. Count the electrons around each atom: are the octets complete? If so, your Lewis dot structure is complete. 5. If the octets are incomplete, and more electrons remain to be shared, move one electron per bond per atom to make another bond. Note that in some structures there will be open octets (example: the B of BF3), or atoms which have ten electrons (example: the S of SF5).

beta particle

A beta particle (also written as β-particle) is the same as an electron. It is often called a high energy electron because it is very fast moving. A beta particle comes from the nucleus of an atom! It has a charge of -1 and very little mass

Be able to classify matter as heterogeneous, homogeneous solutions, and homogeneous suspensions.

A heterogeneous mixture is a nonuniform mixture in which the components separate and the composition varies. Unlike the homogeneous mixture, heterogeneous mixtures can be separated through physical processes. A homogeneous mixture is one in which the composition of its constituents are uniformly mixed throughout. A homogeneous mixture in which on substance, the solute, dissolves completely in another substance, the solvent, may also be called a solution. A homogeneous suspension of material means that when dividing the volume in half, the same amount of material is suspended in both halves of the substance.

molecule

A neutral group of atoms held together by covalent bonds

photon

A particle of electromagnetic radiation with no mass that carries a quantum of energy. A bundle of light energy that is emitted as an electron in an excited state relaxes from a higher energy level to its normal, lower energy level.

electron

A subatomic particle that has a negative charge.

alpha-decay

Alpha decay is one process that unstable atoms can use to become more stable. During alpha decay, an atom's nucleus sheds two protons and two neutrons in a packet that scientists call an alpha particle. Since an atom loses two protons during alpha decay, it changes from one element to another.

Know how the three types of radiation act in a magnetic field and how to protect yourself from each.

Alpha: these are fast moving helium atoms. They have high energy, typically in the MeV range, but due to their large mass, they are stopped by just a few inches of air, or a piece of paper. Beta: these are fast moving electrons. They typically have energies in the range of a few hundred keV to several MeV. Since electrons are might lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals. Gamma: these are photons, just like light, except of much higher energy, typically from several keV to several MeV. X-Rays and gamma rays are really the same thing, the difference is how they were produced. Depending on their energy, they can be stopped by a thin piece of aluminum foil, or they can penetrate several inches of lead.

Is an element with a long or short half-life more dangerous to your health?

An element that has a short-life because it emits more radiation because the atoms decay faster.

strong nuclear force

As its name implies, it is the strongest of the four. However, it also has the shortest range, meaning that particles must be extremely close before its effects are felt. Its main job is to hold together the subatomic particles of the nucleus (protons, which carry a positive charge, and neutrons, which carry no charge. These particles are collectively called nucleons).

What is an orbital? How many electrons can each orbital hold?

Atomic orbitals are regions of space around the nucleus of an atom where an electron is likely to be found. Atomic orbitals allow atoms to make covalent bonds. energy level: 1,2,3,4,5,6 shell letter: k,l,m,n,o,p electron capacity: 2,8,18,32,50,72

carbonate

CO3 2-

ionization energy

Electrons are attracted to the nucleus of an atom, so it takes energy to remove an electron. The energy required to remove an electron from an atom is called the first ionization energy. Once an electron has been removed, the atom becomes a positively charged ion (cation). The energy required to remove the next electron from the ion is called the second ionization energy, and so on.

What is ionization energy? Rank elements according to change in ionization energy.

Electrons are attracted to the nucleus of an atom, so it takes energy to remove an electron. The energy required to remove an electron from an atom is called the first ionization energy. Once an electron has been removed, the atom becomes a positively charged ion (cation). The energy required to remove the next electron from the ion is called the second ionization energy, and so on. Increases from left to right and from bottom to top.

valence electron

Electrons in the highest occupied energy level of an element's atoms; determines the chemical properties of an element. To find this amount look at an items group #. These are usually the only electrons involved in chemical bonds.

How do we get power from nuclear fission or fusion?

Fission is a reaction when the nucleus of an atom, having captured a neutron, splits into two or more nuclei, and in so doing, releases a significant amount of energy as well as more neutrons. These neutrons then go on to split more nuclei and a chain reaction takes place. Fusion is a process where nuclei collide and join together to form a heavier atom, usually deuterium and tritium. When this happens a considerable amount of energy gets released at extremely high temperatures: nearly 150 million degrees Celsius. At extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma—a hot, electrically charged gas.

electromagnetic spectrum

Full range of frequencies and wavelengths for electromagnetic waves broken down into the following region, in order of descending/decreasing λ: radio, infrared, visible light, ultraviolet, X-ray, Gamma Ray.

gamma ray

Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum.

Know how half-lives work for radioactive elements and how you can determine some things age by its remaining radioactivity.

Half life can be defined as the time taken for the number of nuclei in a radioactive material to halve. It can also be defined as the time taken for the count rate of a sample of radioactive material to fall to half of its starting level.

What is an atomic spectrum? Why is it not continuous? How do photons interact with electrons? When is light given off?

High-energy photons are going to look like higher-energy colors: purple, blue and green; whereas lower-energy photons are going to be seen as lower-energy colors like red, orange and yellow. Remember those colors of the rainbow - red, orange, yellow, green, blue and violet? Those are listed in the order of increasing energy. Essentially, each transition that this hydrogen electron makes will correspond to a different amount of energy and a different color that is being released.

nuclear fission

In nuclear fission the nucleus of an atom breaks up into two lighter nuclei. The process may take place spontaneously in some cases or may be induced by the excitation of the nucleus with a variety of particles (e.g., neutrons, protons, deuterons, or alpha particles) or with electromagnetic radiation in the form of gamma rays.

beta-decay

In nuclear physics, beta decay (β decay) is a type of radioactive decay in which a proton is transformed into a neutron, or vice versa, inside an atomic nucleus. This process allows the atom to move closer to the optimal ratio of protons and neutrons.

nuclear fusion

In nuclear physics, nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at a very high speed and join to form a new type of atomic nucleus. During this process, matter is not conserved because some of the matter of the fusing nuclei is converted to photons (energy).

Know the properties of visible light and what a photon is.

Light is electromagnetic radiation that has properties of waves. The electromagnetic spectrum can be divided into several bands based on the wavelength. visible light represents a narrow group of wavelengths between about 380 nm and 730 nm. ultraviolet, violet, blue, green, yellow, orange, red, infrared. A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. A bundle of light energy that is emitted as an electron in an excited state relaxes from a higher energy level to its normal, lower energy level.

ammonium

NH4 +

nitrite

NO2 -

nitrate

NO3 -

hydroxide

OH -

valence shell

Outer shell that determines if electrons will be given, taken, or shared. The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.

phosphate

PO4 3-

electron-dot tructure

Pictorial representation of the valence electron configuration around an atom.

wavelength

Quantity Equal to the distance between any two equivalent consecutive points along a wave, such as two consecutive crest peaks, expressed as λ.

sulfite

SO3 2-

sulfate

SO4 2-

effective nuclear force

The effective nuclear charge is the net positive charge experienced by valence electrons. It can be approximated by the equation: Zeff = Z - S, where Z is the atomic number and S is the number of shielding electrons.

Be able to determine an elements number of inner-shell electrons. It's effective nuclear charge.

The group number of an element in the periodic table is the same as the number of electrons in its outer shell.is the net positive charge experienced by valence electrons. It can be approximated by the equation: Zeff = Z - S, where Z is the atomic number and S is the number of shielding electrons.

inner shell shielding

The tendency of inner-shell electrons to partially shield outer-shell electrons from the attractive pull exerted by the positively charged nucleus

quantum

a discrete packet of energy or matter. Also means the minimum value of a physical property involved in an interaction. For example: the quantum of charge is the charge of an electron.

nonbonding pair

a lone pair refers to a pair of valence electron that are not shared with another atom and is sometimes called a non-bonding pair. Lone pairs are found in the outermost electron shell of atoms. They can be identified by using a Lewis structure.

proton

a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.

neutron

a subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.

ion

is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge.

wave frequency

is measured in the hertz unit. Is the number of waves that pass by per second.

When would you use a physical model? A conceptual one?

physical, conceptual

polyatomic ion

polyatomic ion, also known as a molecular ion, is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit.

alpha particle

positively charged particle, identical to the nucleus of the helium-4 atom, spontaneously emitted by some radioactive substances, consisting of two protons and two neutrons bound together, thus having a mass of four units and a positive charge of two.

What are the necessary factors to have a good sustained chain reaction? What needs to be produced from the splitting of an atom to keep a chain reaction going and supply a lot of power?

proper conditions for a chain reaction depend not only on various external factors, such as temperature, but also on the quantity and shape of the substance undergoing the reaction. In order to sustain a chain reaction, a sample must be large enough to slow the neutrons so that one can be captured by another nucleus and produce a second fission. The sample must also be compact to prevent neutrons from escaping.

Know some of the common uses of radioactive elements.

smoke detectors, watches and clocks, ceramics, glass, fertilizer, food

What forces keep a nucleus together?

strong nuclear force, a short-range force between nucleons. At very small separations, the nuclear force is repulsive, keeping the protons and neutrons from getting too close to one another.

critical mass

the amount of material that must be present before a chain reaction can sustain itself. It is used to refer generally to the minimum amount of something needed to produce a given effect.

half-life

the half-life of an isotope refers to the time it takes for one-half of the sample to decay.

Be able to complete a decay equation given the reactant and one product or both products.

the lower number is the atomic number and the upper number is the mass number. or α-decay, is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or 'decays' into an atom with a mass number that is reduced by 4 and an atomic number that is reduced by 2.When a radioactive nucleus disintegrates by emitting a beta-particle, the atomic number decreases by one and the mass number remains the same.

If an element undergoes alpha or beta decay be able to predict the product.

the lower number is the atomic number and the upper number is the mass number. or α-decay, is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or 'decays' into an atom with a mass number that is reduced by 4 and an atomic number that is reduced by 2.When a radioactive nucleus disintegrates by emitting a beta-particle, the atomic number decreases by one and the mass number remains the same.

atomic spectrum

the spectrum of frequencies of electromagnetic radiation emitted or absorbed during transitions of electrons between energy levels within an atom. Each element has a characteristic spectrum by which it can be recognized.

What happens when there are too many neutrons in the nucleus and not enough protons?

unstable

Why are the elements larger than lead always unstable?

with large elements, it becomes more difficult for the strong nuclear force to overcome the electrostatic repulsion between protons.