Chapter 4: Chemical bonding Flashcards
What is chemical bonding?
- Chemical bonding occurs due to the transfer/sharing of electrons between atoms in order to achieve the electronic configuration of a noble gas.
Why do noble gas have stable electronic configurations?
- This is because of their completely filled electron shells.
- E.g. Helium
Electronic configuation: 2 - E.g. Neon
Electronic configuration: 2,8 - E.g. Argon:
Electronic configuration: 2,8,8
What is a noble gas configuration?
- A noble gas configuration is made out of 2 electrons in the first electron shell, followed by 8 electrons each in the second and third electron shells.
- E.g. Helium; which has one completely filled electron shell, has a DUPLET electronic configuration.
- E.g. Neon and argon; which has 2 and 3 completely filled electron shells respectively, have an OCTET electronic configuration.
What happens when there is a stable configuration?
- Due to their stable configurations, noble gases do not form chemical bonds and they usually exist as a single atom or are MONATOMIC.
How do we achieve a completely filled valence/outermost shell of electrons?
- The atoms of all other elements in the periodic table lose/gain/share electrons.
Where are metals mainly found in the periodic table?
- Metals are mainly found in groups 1-3 of the periodic table.
What happens when atoms of METALS have less than 4
valence /outermost electrons?
- As atoms of metals have less than 4 valence/outermost electrons, they tend to lose electrons, which are transferred to atoms of non-metals.
Where are non-metals mainly found in the periodic table?
- Non-metals are mainly found in groups 14-17 of the periodic table.
What happens when atoms of NON-METALS have less than 4
valence /outermost electrons?
- As atoms of non-metals usually have 4 or more than 4 valence electrons, they tend to gain electrons from atoms of metals/share electrons with atoms of other non-metals.
How are ions formed?
- Ions are formed when atoms gain or lose electrons.
How are anions formed?
- Anions are formed when non-metals gain electrons.
How are cations formed?
- Cations are formed when metals lose electrons.
- E.g. A magnesium atom loses 2 electrons to form a magnesium ion, and an oxygen atom gains 2 electrons to form an oxygen (O2) ion.
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SEE MAGNESIUM AND OXYGEN’S gain/loss of electrons and noble gas electronic configuration IN NOTEBOOK!
What are ionic bonds?
- Ionic bonds refer to the electrostatic attraction between cations and anions.
- Thus, an ionic compound is formed.
- E.g. Magnesium reacts with oxygen to form the ionic compound, and magnesium oxide and magnesium oxide can be represented using a DOT-and CROSS diagram.
Are ionic compounds neutral? How does it benefit the/its compound?
- Ionic compounds are electrically NEUTRAL, so this means that the total charge of the cations cancels out the total charge of the anions.
- Thus, the ratio of the cations and anions required to form an ionic compound can be determined/estimated.
What are polyatomic ions?
- Polyatomic ions are ions that are made up of 2 or more atoms covalently bonded together.
- E.g. The ammonium ion (NH4+) and the sulfate ion (SO4 2-)
**A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms
What is a giant ionic crystal lattice?
- A giant ionic crystal lattice is where, an ionic compound in the solid state that has oppositely charged ions, is arranged REGULARLY.
- In the ionic compound sodium chloride (NaCl):
- the Na+ ions and cl ions are arranged alternately to prevent the repulsion in a 3-dimensional structure.
- Each cation is surrounded by 6 anions and vice versa
- Strong electrostatic forces of attraction exist between the oppositely charged ions, thus holding the structure together.
How do atoms achieve the noble gas configuration?
-Atoms share electrons to achieve the noble gas configuration.
How is a covalent bond formed?
- A covalent bond is formed when 2 electrons are shared between the 2 atoms.
- Thus, 2 covalent bonds are formed when 4 electrons are shared between 2 atoms, etc.
- E.g. A hydrogen atom has 1 valence electron, and it shares 1 electron with another hydrogen atom to achieve an outermost shell completely filled with 2 valence electrons. Thus, a single covalent bond is formed between the 2 HYDROGEN atoms.
** A single covalent bond is made up of 2 electrons. - E.g. an oxygen atom has 6 valence electrons, and it shares 2 electrons with another oxygen atom to achieve an outermost shell completely filled with 8 valence electrons. Thus, a double covalent bond is formed between the 2 OXYGEN atoms.
** A double covalent bond is made up of 4 electrons.
How are diatomic molecules formed?
- Diatomic molecules are formed when 2 atoms are covalently bonded together.
- E.g. Hydrogen (H2), nitrogen (N2), oxygen (O2), and chlorine (Cl2).
What are the 2 different scenarios that covalent bonding ca occur between?
- Atoms of the same element form molecules of the element.
(E.g. H2, N2, O2) - Atoms of different elements form molecules of a compound.
(E.g. H2O, CO2, NH3)
Example 1:
* A water molecule (H2O) molecule consists of 2 hydrogen atoms and 1 atom covalently bonded together. *
- A hydrogen atom has 1 valence electron, and it requires 1 more electron to achieve 1 noble gas electronic configuration.
- An oxygen atom has 6 valence electrons, and it requires 2 or more electrons to achieve a noble gas electronic configuration.
- 2 hydrogen atoms each share 1 electron with an oxygen atom to achieve a noble gas electronic configuration.
What happens when a molecule consists of 3 or more atoms?
- If a molecule consists of 3 or more atoms, the atom that forms the most number of bonds will be the central atom in the molecule.
- E.g. In a water molecule, the oxygen atom forms 2 covalent bonds with the hydrogen atoms, while each hydrogen atom forms 1 covalent bond with the oxygen atom. Thus, oxygen is the central atom in the water molecule.
How are atoms of metals and cation arranged?
- Atoms of metals lose electrons to form cations.
- The cations are arranged in an orderly manner and are surrounded by a “sea of delocalised electrons” (are free to move in the lattice) in a giant metallic lattice.
What are metallic bonds?
- Metallic bonds are the strong electrostatic forces of attraction that exist between cations and the “sea of delocalised electrons”.
Example: - Sodium loses its valence electron to achieve a stable electronic configuration. *
- The electron that is lost is NO longer in the metal atom, it is mobile, and it moves around in the metallic lattice, and this is known as delocalisation.
- There are strong electrostatic forces of attraction between the sodium ions, and the delocalised electrons in the giant metallic lattice.
What is delocalisation?
- Delocalisation is the process when the electron that is lost is NO longer in the metal atom, it is mobile, and it moves around in the metallic lattice.
