Which is the most stable Lewis structure for COCl2?
Answer: The most stable structure for
COCI2 is Structure A.
Differences between Single, Double and Triple Bond
 |
| comparison of bond length |
- Multiple bonds are shorter than single covalent bonds.
- Double and triple covalent bonds are stronger than single covalent bonds and they are characterized by the sharing of four or six electrons between atoms, respectively.
- Double and triple bonds are comprised of sigma bonds between hybridized orbitals, and pi bonds between unhybridized p orbitals.
- Double and triple bonds offer added stability to compounds, and restrict any rotation around the bond axis.
- Bond lengths between atoms with multiple bonds are shorter than in those with single bonds.
- Bond length is defined as the distance between the nuclei of two covalently bonded atoms in a molecule.
- For a given pair of atoms such as carbon and nitrogen, triple bonds are shorter than double bond, which, in turn are shorter than single bond.
Single Bond, Double Bond and Triple Bond
Single Bond
- A covalent bond formed when 2 atoms share a pair of electron
- Represent by dash (-) between 2 atoms
- A single bond is made up of a sigma (σ) bond
- Example: HCl and HF
Double Bond
- A covalent bond formed when 2 atoms share 2 pairs of electron
- Represent by double dash (=) between 2 atoms
- A double bond is made up of sigma bond (σ) and pi bonds (π)
- Example: O2
- A covalent bond formed when 2 atoms share 3 pairs of electron
- Represent by triple dash (Ξ) between 2 atoms
- A triple bond is made up of 1 sigma bond (σ) and 2 pi bonds (π)
- Example: N2
Properties of Ionic or Electrovalent Compound
 |
| Example of ionic or electrovalent compound |
- Solid at room temperature
- High melting/ boiling point
- Soluble in water
- Molten ionic compounds conduct electricity because they contain mobile ions (cations & anions)
STPM Chemistry: Atoms, Molecules and Stoichiometry [Checklist]
- Electron: A subatomic particle that has a very low mass and carries a single negative electric charge.
- Neutron: A subatomic particle that bears no net electric charge. Its mass is slightly greater than a proton’s.
- Proton: A subatomic particle having a single positive electric charge. The mass of a proton is about 1840 times that of an electron.
- Nucleus: The central core of an atom.
- Nucleon number (mass number) Symbol A: The total number of protons and neutrons found in the nucleus of an atom.
- Avogadro’s number (NA): 6.02 X 1023; the number of particles in a mole.
- Relative atomic mass, Ar, is defined as the mass of one atom of an element relative to 1/12 of the mass of an atom of carbon-12, which has a mass of 12.00 atomic mass units.
- Relative isotopic mass is like relative atomic mass in that it deals with atoms. The difference is that we are dealing with different forms of the same element.
- Isotopes have the same number of protons, but different numbers of neutrons. Hence, isotopes of an element have different masses.
- Relative molecular mass, Mr, is defined as the mass of one molecule of an element or compound relative to 1/12 of the mass of an atom of carbon-12, which has a mass of 12.00 atomic mass units.
- Relative formula mass is used for substances that do not contain molecules, such as sodium chloride, NaCl, and is the sum of all the relative atomic masses of the atoms present in the formula of the substance.
- It is important to remember that since these are all relative masses, they have no units.
- Mole: The amount of substance which contains 6 × 1023 atoms, ions or molecules. This number is called
- Avogadro’s constant.
- Empirical formula: A formula showing the simplest ratio of atoms present.
- Molecular formula: A formula showing the actual number of atoms of each element present in one molecule.
What is electron affinity?
Electron affinity reflects
the ability of an atom to accept an electron. It is the energy change that
occurs when an electron is added to a gaseous atom.
- These reactions tend to be exothermic (release energy) because an electron approaching a neutral atom experiences an attraction for the positively charged nucleus.
- So the values of EA are generally negative. The higher (more negative) the EA, the more easily it accepts an electron.
- The smaller the atom, the closer an added electron can approach the atomic nucleus and the more strongly it is attracted to the nucleus.
- However, affinity does not always release energy. In some cases affinity requires energy.
Mole Concept
- A mole is defined as the amount of substance which contains equal number of particles (atoms / molecules / ions) as there are atoms in exactly 12.000g of carbon-12.
- One mole of carbon-12 atom has a mass of exactly 12.000 grams and contains 6.02 x 1023 atoms.
- The value 6.02 x 1023 is known as Avogadro Constant.
