# Structure and bonding in applications of science

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• Structure and bonding in applications in science.
• The electronic structure of atoms.
• The nucleus contains the protons and neutrons. The electron orbit the nucleus in shells.
• Relative charge - Proton = +1 Neutron = 0  Electron = -1
• Relative mass - proton = 1     neutron = 1    electron = Very small (1/1840)
• Atoms are neutral (they have no overall charge)
• Therefore the number of protons = the number of electrons.
• Atomic number = number of protons in the nucleus of an atom.              Mass number = protons + neutrons
• Number of protons = the atomic number of the atom.
• Number of electrons= same as the number of protons in the atom (not an ion).
• Number of neutrons = mass number - atomic number
• Group number = electrons in the outer shell                  Period number = number of shells
• Electronic structure and orbitals.
• A shell is also known as an energy level.
• Shells contain subshells which contain orbitals.
• An orbital is a region of space where an electron is likely to be found and each orbital holds 2 electrons.
• The size of the shell determines how many subshells it can contain.
• An s subshell has 1 orbital and can therefore hold 2 electrons.     A p subshell has 3 orbitals and can therefore hold 6 electrons.     A d subshell has 5 orbitals and can therefore hold 10 electrons.
• Bohr theory
• Electrons exist in fixed energy levels.
• An electron can exist in the 1st energy level or the 2nd energy level but it cannot exist somewhere in between.
• An electron can move to a higher energy level by absorbing radiation.
• An electron can fall to a lower level emitting radiation.
• Ionic bonding
• Ionic bonding occurs between a metal and a non-metal.
• When the atoms react the metal atom loses electrons and the non-metal atom gains electrons. The atoms then become ions.
• An ion is something that has gained or lost an electron. Positive ions have lost electrons.
• The result of the electrostatic attraction between a positive and negative ion.
• Structure= a giant ionic lattice in which many ions are held together by strong electrostatic attractions.
• Ionic compounds have high melting and boiling points because of the giant lattice structures and there is a strong electrostatic attraction between the positive and negative ions.
• Ionic compounds don't conduct electricity when solid because ions cannot move.
• Ionic compounds conduct electricity when melted or in solution because the ions are free to move.
• The strength of the ionic bond is down to the attraction between the positive and negative ion. The bigger the attraction the greater the strength of the ionic bond.
• The more shells an ion has the bigger the ion will be.
• The size of the ion increases as you go down a group.
• The more protons in the nucleus the smaller the ion.
• The size of the ion decreases as there are more protons in the nucleus.
• Covalent bonding
• A covalent bond is formed between two non-metals.
• There is a strong electrostatic attraction between the two nuclei and the shared pair of electrons.
• Dative covalent
• Formed when both electrons in the shared electron pair come from one atom.
• Atoms that donate:     group 5,6,7      Atoms that Accept: H+ and group 3.
• Single covalent bonds
• 1 electron pair is shared.Weakest and longest type of bond.
• Double covalent bond
• 2 electron pairs are shared.
• Triple covalent bond
• 3 electron pairs are shared. strongest and shortest type of bond.