Energy, elements, atoms and molecules Flashcards
What is Avogadro’s constant?
number of protons per gram (6.02 x10^23)
Concentration of hydrogen ions in water
the concentration of hydrogen ions in water is 1x10^-7
Define anabolism
A sequence of chemical reactions that synthesizes molecules from smaller units
Describe the bonding of a water molecule
In a water molecule, a covalent bond forms as the two hydrogen atoms share an electron with the oxygen. These additional two electrons allow oxygen to fill its 2p orbitals making it more stable. The covalent bonds in water are single and polar. Because oxygen is more electronegative than hydrogen, the region around oxygen has a partial negative charge and the region near the two hydrogen atoms has a partial positive charge allowing the formation of hydrogen bonds with other polar molecules.
pH equation
pH = -log [H + ]
Examples of kinetic energy
movement and heat
Define: Atom
Smallest unit of matter which still retains the properties of an element; made of subatomic particles (Protons and neutrons in nucleus and electrons in clouds around the nucleus)
Define: Catabolism
Breaking down complex molecules into smaller ones
Define: Compound
Substance consisting of two or more elements in a fixed ratio
Define: Covalent bonds
Sharing of electrons by two atoms: polar (not equal sharing) eg. Water or non-polar (equal sharing). Strong around 400 kJ/mol
Define: Electronegativity
the tendency of an atom to attract an electron
Define: Element
A substance which cannot be broken down to other substances by chemical reactions.
Define: Heat of vapourisation
Energy to convert 1g of water from liquid to gas at 25°C
Define: Hydrogen bonds
Molecules with polar bonds; are weak compared to ionic/covalent (10-20 kJ/mol) but are strong when together. Hold together the structure of DNA
Define: Ionic bonds
Form between two very different atoms in attraction for the valence electrons come together; for a crystal. Very strong 700kJ/mol
Define: Isotope
Different mass number of an element but same atomic number ; Number of neutrons have no effect on the chemical properties so are chemically identical hence are the same element but has different masses
Define: Metabolism
The sum of the chemical reactions that take place within each cell of a living organism; provide energy for all vital reactions
What is molarity or M?
a unit to measure concentration (moles of solute per litre of solution).
Define: Moles
a unit defined as the number of atoms within 12g of carbon-12 (6.02 x10 23 )
Define: Orbitals
Contain no more than 2 electrons, more stable when filled than unfilled. Elements ‘try’ to lose/ gain electrons in order to obtain filled orbitals
Define: Polarity
Caused by differences in electronegativity of atoms within a molecule; allows interaction and bonding eg. Hydrogen bonding
Define potential energy
Energy possessed because of a position eg.chemical energy
What are valence electrons?
Directly involved in reactions; form bonds
Define van der waal’s forces
Very weak (0.5kJ/mol), short range, collectively strong. The movement and position of the electrons cause an interaction between electron clouds
