Animal Metabolism –
Chemical reactions in animals
? Polar molecules interact through dipole-dipole intermolecular forces and hydrogen bonds. A polar bond is where the electrons forming the bond are unevenly distributed. Causing a slight electrical dipole moment in the molecule, where one end is slightly positive and the other slightly negative.
? Water (H2O)
? The hydrogen atoms are both on one side of the oxygen atom, rather than evenly spaced. The oxygen side of the molecule has a slight negative charge, while the side with the hydrogen atoms has a slight positive charge.
? H2O is held together by hydrogen bonds, which is the intermolecular forces and have strong but temporary covalent bonds (intramolecular).
? The electronegativity values are 2.2 for hydrogen and 3.44 for oxygen, meaning the electronegativity difference is 1.24, showing that it is has polar covalent bonds.
? The electronegativity difference is significant enough between the oxygen and carbon atoms that there is an asymmetric distribution of electrons.
? Glucose has all three types of intermolecular forces because it is polar so it has Dipole-Dipole, London forces are in every molecule, and Hydrogen because if another Glucose Molecule came around the Hydrogens would be attracted to the Oxygens. With ionic bonds as the intramolecular forces.
? The electronegativity values are 2.5 for carbon, 2.2 for hydrogen, and 3.5 for oxygen. This means the difference is 3 showing it has polar ionic bonds.
? Polar substances will have a higher viscosity, lower vapour pressure, and higher boiling point due to the dipole-dipole interaction between polar molecules results in stronger intermolecular attractions.
? A substance must have charge asymmetry and geometric asymmetry for it to be non-polar.
? is a linear molecule and the Oxygen (O) atoms on each end are symmetrical. Polarity results from an unequal sharing of valence electrons (outer shell electrons). Because of this symmetry there is no polarity and CO2 is a nonpolar molecule.
? Therefore, the only intermolecular forces are London dispersion forces.
? The intramolecular force present is the two covalent bonds from each oxygen atom to the middle carbon atom
? The electronegativity values are 3.5 for oxygen and 2.5 for carbon, making the electronegativity difference 1. This shows it has covalent bonds, however because of the symmetry of the molecule it is nonpolar.
? has four Carbon-Hydrogen single covalent bonds (intramolecular forces). These covalent bonds are called nonpolar covalent bonds because the outcome of this equal sharing of electrons is that there is no dipole moment.
? The only intermolecular forces in methane are London dispersion forces as it is a non-polar molecules.
? The electronegativity values are 2.5 for carbon and 2.1 for hydrogen, making the electronegativity difference 0.4, showing that it has nonpolar covalent bonds.
? Due to the charge asymmetry the substance will be more stable – less likely to react – which is seen when a non-polar substance at room temperature, such as gasoline, is added to a polar substance, such as water. Following the ‘like dissolves like’ rule, the gasoline is insoluble due to the lack of polar molecules. This results in a hydrophobic compound.
? When compared to a polar molecule with a similar molar mass, a non-polar molecule will generally have a lower boiling point and surface tension, due to the weakness of the intermolecular forces it forms.
? Intermolecular –
? These are the forces that mediate interaction between molecules, including forces of attraction or repulsion which act between molecules and other neighbouring particles such as; atoms or ions.
? The intermolecular forces arise due to the presence of dipoles in the molecules, including permanent dipoles, instantaneous dipoles, and induced dipoles.
? Hydrogen Bonding is a strong intermolecular force that involves three features:
? A large dipole between a hydrogen atom and a highly electronegative atom.
? The small hydrogen atom which can get very close to other atoms.
? A lone pair of electrons on another O, N or F atom, with which the positively charged H atom can line up
? Intramolecular –
? An intramolecular force is any force that holds together the atoms making up a molecule or compound. This includes all types of chemical bonds.
? They are usually stronger than intermolecular forces, which are present between atoms or molecules that are not bonded.
Bond Strength How’s it formed Diagram
Ionic (intra) The strongest of chemical bonds. 600–4000 kJ/mol A complete transfer of valence electrons between atoms.
Covalent (intra) One of the two strongest chemical bonds. 150–400 kJ/mol This bond is formed between atoms that have similar electronegativity’s.
Metallic (intra) Strong but not as significantly as covalent. 350-500 kJ/mol This bond is formed by the attraction of the mobile electrons and the fixed positively charged metal ions.
Dipole-dipole (inter) Much weaker than intramolecular forces.
5 to 20 kJ/mol These forces occur when the partially positively charged part of a molecule interacts with the partially negatively charged part of the neighboring molecule.
Hydrogen (inter) Much weaker than intramolecular forces.
4 to 40 kJ/mol This occurs specifically between a hydrogen atom bonded to either an oxygen, nitrogen, or fluorine atom.
London dispersion forces (inter) Much weaker than intramolecular forces These are the weakest of the intermolecular forces and exist between all types of molecules, whether ionic or covalent—polar or nonpolar.
• All substances are made from atoms.
• Each atom is made of a nucleus – containing protons and neutrons – surrounded by electrons.
• The atomic number is the number of protons in an atom, which will always be the same as the number of electrons unless it is an isotope.
• The atomic number of the nucleus defines the element. The number of neutrons added to the number of protons is the nucleon number or atomic mass.
• To calculate amount of electrons that fill each shell you use the 2n² rule, where n is the shell number
• Oxygen has 8 protons, 8 neutrons, and 8 electrons meaning it has an atomic mass of 16 amu.
• The first electron shell is always filled by 2 electrons and the second with 8, therefore in the case of this atom the electronic configuration would be 1S22S6.
• Oxygen has the same number of protons and electrons, meaning it has no overall charge.
• Carbon has 6 protons, 6 neutrons, and 6 electrons meaning it has an atomic mass of 12 amu.
• The first electron shell is always filled by two electrons and the second with 8, therefore in the case of this atom the electronic configuration would be 1S22S4.
• Carbon has the same number of protons and electrons, meaning it has no overall charge.
• Descending a group
• The first ionisation energy decreases on going down a group.
• This is because the electron to be removed from the outer energy level is increasingly distant from the nucleus, as a result of the atoms getting bigger.
• The attraction of the nucleus for the electron becomes less, and it becomes easier to pull it away.
• Electrons in the inner energy levels also produce a screening effect. These inner electrons reduce the attraction of the nucleus for the outer electrons. The screening effect will increase as the number of inner energy levels increases.(see graph on next slide)
• Crossing a period
• The first ionisation energy generally increases on going across a period.
• This is because on crossing a period, more protons are being added to the nuclei of the atoms. This results in an increase in nuclear charge.
• The electrons in the outer energy levels will be more tightly held, and more difficult to remove.
• Ionisation is a process in which atoms lose or gain electrons and become ions.
• Looking at trends in ionisation energies can reveal useful evidence for the arrangement of electrons in atoms and ions.
• The first ionisation (I1) energy of an element is the energy required to remove one electron from a gaseous atom.
• The second ionisation (I2) energy involves the removal of a second electron
• Large jumps in the ionisation energy reveal where electrons are being removed from the next principal energy level
• The ionisation process, by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules, contributes to molecule formation
• This is because once ionised the atom will have a slightly positive or negative charge, meaning it is more likely to react with anther atom to gain or loose an electron to become stable again.
• Electron shielding also contributes to molecule formation because the more inner electron shells shield the nuclear charge from the outer electron, the electron is easier to remove. Shielding increases down a group.
Animal Metabolism –