Atomic structure Flashcards
Mass number (A)
total number of protons and neutrons in the nucleus of an atom
Atomic (proton) Number (Z)
number of protons in the nucleus of an atom
– it identifies the element
All atoms of the same element have the same number of protons
Atoms
neutral atoms which have no overall charge the number of electrons is the same as the number of protons. The number of neutrons is just mass number minus atomic number
Ions
Atoms form ions by gaining or losing electrons. Ions have different numbers of protons and electrons — negative ions have more electrons than protons, and positive ions have fewer electrons than protons.
Anions
ion that has gained one or more electrons, acquiring a negative charge
Cations
ion that has lost one or more electrons, acquiring a positive charge
Zwitterion
molecule with functional groups, of which at least one has a positive and one has a negative electrical charge. The net charge of the entire molecule is zero
Isotopes
element are atoms with the same number of protons but diff number of neutrons. E.G chlorine-35 and chlorine-37 are examples of isotopes.
They have different mass numbers, so they have different numbers of neutrons.
Their atomic number is the same.
Radioisotopes
radioactive isotopes of an element.
They can also be defined as atoms that contain an unstable combination of neutrons and protons, or excess energy in their nucleus.
Radioactive isotopes have many useful applications.
In medicine, for example, cobalt-60 is extensively employed as a radiation source to arrest the development of cancer.
Other radioactive isotopes are used as tracers for diagnostic purposes as well as in research on metabolic processes.
The decay of radioactive elements
occurs at a fixed rate
The half-life of a radioisotope
time required for one half of
the amount of unstable material to degrade into a more stable material.
For example, Co-60 has a half-life of about 5 years while Ir-192 has a half-life of about 74 days
Electron shells
Electrons have fixed energies. They move around the nucleus in certain areas of the atom called shells or energy levels. Each shell is given a number called the principal quantum number.
The further a shell is from the nucleus, the higher its energy and the larger its principal
quantum number.
Shells are divided up into
subshells.
Different electron shells have different numbers of sub-shells, which each have a different energy.
Subshells can be s sub-shells, p sub-shells, d sub-shells or f sub- shell
Nuclear Force
force that binds the protons and neutrons in a nucleus together.
This force can exist between protons and protons, neutrons and protons or neutrons and neutrons.
This force is what holds the nucleus together
Electromagnetic Force
Also called ‘the Lorentz force’, acts between charged particles, like negatively charged electrons and positively charged protons.
Opposite charges attract one
another, while like charges repel.
The greater the charge, the greater the force.
Electronic Configurations
number of electrons that an atom or ion has, and how they are arranged is called its electron configuration.
It can be shown three ways.
Aufbau Principle
electrons will occupy lowest energy orbital available
Pauli’s Exclusion Principle
maximum of 2 electrons can occupy a single orbital
Hund’s rule
e’s with same spin must occupy an orbital of equal energy before additional e’s with opposite spins can occupy the same orbital
Periodic table
arranged into periods (rows) and groups(columns) by proton (atomic) number
All the elements within a period
same number of electron shells (not counting subshells)
All elements within a group
same number of electrons in their outer shell – so they have similar properties.
The group number tells you the number of electrons in the outer shell.
exception to groups rule
group 0
All group 0 elements have 8 electrons in their outer shells apart from helium, which has two giving them full outer shells.
Atomic Radius
decreases across a period. As the number of protons increases, the positive charge of the nucleus increases.
This means electrons are pulled closer to the nucleus making the atomic radius smaller.
The extra electrons that the elements gain across a period are added to the outer energy level, so they don’t really provide any extra shielding effect.
(Shielding is mainly provided by the electrons in the inner shells).
As you go down a group in the periodic table, the atomic radius gets larger.
This is because extra electron shells are added as you go down the group.
The Shielding Effect
Electrons are attracted to protons in the nucleus of an atom.
The closer the electron is to the nucleus, the stronger the force of attraction.
The more protons in a nucleus, the more strongly an electron is
attracted to the nucleus.
Electrons are repelled by other electrons within an
atom.
If there are other electrons between a valence (outer) electron and the nucleus, the valence electron will be less attracted to the nucleus
Electronegativity
the ability an atom has to attract other electrons.
As
you go across a period the electronegativity increases.
This is because the nuclear charge increases, and the atomic radii decreases.
There are more electrons but the increase in shielding is negligible because each extra electron enters the same shell so electrons will be more strongly attracted to the nucleus.
Going down a group on the periodic table, the
electronegativity of an element decreases because the increased number of energy levels puts the outer electrons very far away from the pull of the nucleus.
Pauling scale
numerical scale of electronegativities based on bond- energy calculations for different elements joined by covalent bonds.
There are no units with electronegativity.
Linus Pauling designed a scale of electronegativity that ranks elements with respect to each other.
So, for example, fluorine is a 4.0 in comparison to 0.7 for francium.
These are the most and least electronegative elements respectively.
