1607 Atomic Structure

What is the basic structure of an atom?

The atom is mostly empty space, similar to our solar system. The nucleus is very small but contains nearly all the mass. Electrons exist in orbital shells.

What are elements, compounds, and molecules?

An element is made up of only one type of atom. A compound is formed by chemically bonding two or more different elements. A molecule consists of more than one atom held together by chemical bonds and is the smallest unit of a compound that can exist by itself and retain all its chemical properties.

What determines an atom's chemical element and behavior?

The number of protons determines the chemical element and ultimately determines chemical behavior. The arrangement of electron shells helps determine how an atom reacts chemically or combines with other atoms.

What are isotopes?

Atoms with the same number of protons but different numbers of neutrons. They behave the same way during chemical reactions.

What does the periodic table show, and what are examples of the first three elements?

The periodic table lists matter in order of increasing complexity, beginning with hydrogen. Hydrogen: 1 proton, 1 electron. Helium: 2 protons, 2 neutrons, 2 electrons. Lithium: 3 protons, 4 neutrons, 3 electrons; 2 electrons in K and 1 in L.

What are electron shells and what are they called?

Electrons can exist only in certain orbital shells representing different electron binding energies. Shells are K, L, M, N, O, P, Q, corresponding to 1–7 and closest to farthest from the nucleus.

What is the maximum number of electrons in each shell?

K-2, L-8, M-18, N-32, O-50, P-72, Q-98. The closer an electron is to the nucleus, the greater its binding energy.

What is uranium's structure?

Uranium has 92 protons and 146 neutrons. Electron distribution: K-2, L-8, M-18, N-32, O-21, P-9, Q-2.

What is ionization?

If an atom has an extra electron or an electron has been removed, it is ionized. Ionization results from electron addition/loss due to collisions with subatomic particles or other atoms, or interaction with electromagnetic radiation.

What particles are involved in ionization?

Only electrons are involved. Changing protons changes the type of atom; changing neutrons does not cause ionization because neutrons are electrically neutral. Except in the lightest atoms, neutrons outnumber protons, with the difference increasing as atoms become larger.

How is the maximum number of electrons in a shell calculated?

2n2, where n is the principal quantum number, representing the location and energy of electrons within an atom. Every electron can be identified by four quantum numbers; the other three represent subshells, which are not important to radiologic science. Example: M-shell = 2(3)2 = 18.

How does electron arrangement relate to the periodic table?

The number of electrons in the outermost shell equals its group (column) and determines valence, the ability to form a chemical bond. The number of the outermost electron shell equals its period (row). No outer shell can contain more than eight electrons.

What happens when the outer shell is filled?

When eight electrons are in the outer shell, the shell is filled. Atoms with filled shells are in group VIII, the noble gases, and are very chemically stable. One outer-shell electron = group I; two = group II; this continues until eight electrons fill the shell.

What are transitional elements?

In the fourth period, electrons are added to an inner shell instead of simply adding them to the next outer shell. These are transitional elements. Their outer shell still cannot contain more than eight electrons, and their chemical properties depend on the electrons in the two outermost shells.

What does shell notation indicate?

It identifies the relative distance of an electron from the nucleus and indicates the relative energy by which the electron is attached to the nucleus.

What forces affect electrons in orbit?

Centripetal force is the “center-seeking” force caused by opposite charges attracting and like charges repelling. Centrifugal force is the “flying-out-from-the-center” force created by electron velocity and allows electrons to maintain their distance while traveling in a circular path.

What is electron binding energy?

The strength of attachment of an electron to the nucleus. The closer an electron is to the nucleus, the more tightly it is bound; K-shell electrons have higher binding energies than L-shell electrons, etc.

How does atom size affect electron binding energy?

Not all K-shell electrons have the same binding energy. The greater the total number of electrons, the more tightly each is bound. Larger and more complex atoms have higher electron binding energy for electrons in a given shell, so more energy is needed to ionize a large atom than a small atom.

What are chemical symbols, atomic number, and atomic mass number?

Chemical symbols are alphabetic abbreviations for elements. Atomic number (Z) = number of protons. Atomic mass number (A) = number of protons + neutrons. In a neutral atom, electrons = protons. Atomic mass number is always a whole number and is not equal to the precise mass of an atom.

What are isotopes, isobars, isotones, and isomers?

Isotopes: same atomic number, different atomic mass numbers. Isobars: same atomic mass number, different atomic numbers. Isotones: same number of neutrons but different protons. Isomers: same atomic number and atomic mass number.

How can isotopes, isobars, isotones, and isomers be remembered?

Isotope = same proton; isobar = same A; isotone = same neutron; isomer = metastable.