Lecture 2 - Basic Chemestry Flashcards
What are the four main elements that make up the human body?
oxygen, hydrogen, carbon, nitrogen
element
A form of matter indivisible by normal means.
compound
Two or more different elements
atom
Smallest particles that retain properties of an element
Atoms are made of what subatomic particles? What are their respective charges?
protons (positive)
neutrons (neutral)
electrons (negative)
Which subatomic particle are represented by atomic numbers?
protons
isotope
Atoms of an element with a different number of neutrons, behave the same as the normal element in chemical reactions
What determines whether atoms will interact with each other?
The number and arrangement of electrons
Properties of electrons
Carry a negative charge
Repel one another
Are attracted to protons in the nucleus
Move in shells (volumes of space surrounding the nucleus)
List the number of electrons in the first three shells of an element
First shell: 2
Second shell: 8
Third shell: 8
chemical bonds
A union between two atoms
valence shell
The outermost shell of an atom.
List the three types of bonds, in order of strength, from strongest to weakest
ionic
covalent (either polar or nonpolar)
hydrogen
Which bonds are held together by charge differences in elements?
ionic bonds, hydrogen bonds
Which bonds are held together by the sharing of electrons?
covalent bonds
What is the difference between polar and non-polar covalent bonds?
In polar covalent bonds, the electrons are not shared equally amongst the elements, with electrons spending more time near the larger nucleus, resulting in a charge differential.
In non-polar covalent bonds, the electrons are shared equally, resulting in no charge difference across the element
If both ionic and hydrogen bonds are held together by charge differentials, what is the difference between them?
Ionic bonds are created though the exchange of an electron, turning two previously neutral elements into a positive and negative one, strongly attracting each other without sharing electrons.
Hydrogen bonds are created when a polar covalently bonded molecule is attracted to an oppositely charged atom.
ionic bond
One atom loses electrons, becoming a positively charged ion, while the atom that gains the lost electrons becomes negatively charged. The charge difference attracts these ions, they do not share the electrons afterwords.
hydrogen bond
Atom in one polar covalent bond attracted to oppositely charged atom in another such molecule or same molecule
List the properties of water
Cohesive - binds to itself Adhesive - binds to other Stabilises temperature Expands when frozen Capacity to dissolve substances
What are hydrogen ions?
Unbound protons that form when water ionises, a hydrogen wtom with no electron
What does pH measure?
The hydrogen ion concentration of a fluid
Describe the pH scale
A scale measured between 0 and 14, with 0 being the highest concentration of hydrogen ions and 14 being the lowest, each integer below 14 represents a 10-fold increase in the number of hydrogen ions present.
acid
Substances which donate hydrogen ions when dissolved in water, have a pH of < 7
base
Substances which accept hydrogen ions when dissolved in water, have a pH of > 7
covalent bond
Atoms share a pair or pairs of electrons to fill the valence shell
buffer system
A partnership between a weak acid and the base it forms when dissolved, working as a pair to counter shifts in pH, minimising the effects.
Identify the reactants and the products of this equation:
2 H2 + O2 -> 2 H2O
H2 and O2 are the reactants, the products are two molecules of water (2 H2O)
Why do water molecules form hydrogen bonds?
It is a polar molecule
What is an elect called that has lost an electron?
An ion
What is an element called that has lost a neutron?
An isotope
Why are the noble gas elements so relatively unreactive?
They possess filled valence shells, making their electrons more stable
