Chapter 31 - Chemical Bonding Flashcards
What is a molecule? (Full book definition please 🌚🌝)
A molecule is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.
GIMME SOME EXAMPLES OF THEM NOW HURRY QUICK TIME IS TICKING GOGOGO
Hydrogen (H2)
Oxygen (O2)
Water (H2O)
Methane (CH4)
Why are the formulas for water and methane H2O and CH4?
Water: Because a molecule of water consists of two hydrogen atoms joined to an oxygen atom
Methane: An atom of carbon joined four atoms of hydrogen
Are the noble gases reactive?
No, they are very unreactive, forming practically no compounds and consisting of single atoms
Note: A sample of helium gas consists entirely of helium atoms, as helium molecules don’t exist
What must an element have to be stable? (Definition)
Elements that have eight electrons in their outer orbit are very unreactive (e.g. the noble gases). The eight electrons in the outer orbit are often referred to as a stable octet.
What is the octet rule?
When bonding occurs, atoms try to have eight electrons in the outer orbit.
This is not a strict chemical law, but is a useful guide to understanding bonding.
What are two exceptions to the octet rule?
- helium only has one occupied orbit of electrons, and it is always full (it’s properties are so similar to the inert gases it’s always classified with them)
- hydrogen and lithium tend to reach the electron configuration of helium when chemical bonding occurs
Why does chemical reaction take place, and what are the two types if chemical bonds formed?
Chemical reaction takes place so the elements can obtain the very stable arrangement of the noble gases.
The covalent and the ionic bond.
What is a covalent bond?
A covalent bond is one that consists of shared electrons
Note: The word ‘covalent’ means ‘sharing’, as the atoms are sharing the electrons to try and get eight in their outer shell/s
What should you not include when using diagrams to explain chemical bonding, and why?
The nucleus, and because chemical bonding only involves electrons.
Give four examples of covalent compounds
- the hydrogen molecule (H2)
- the methane molecule (CH4)
- the water molecule (H2O)
- the oxygen molecule (O2)
- see pages 221+222 of textbook for more in-depth information and diagrams on these*
What is a single bond and when is it formed? (Definition 🤓)
A single bond is formed when one pair of electrons is shared - e.g. H2, CH4
What is a double bond and when is it formed? (Definition 🤔)
A double bond is formed when two pairs of electrons are shared - e.g. O2
What is an ion?
An ion is a charged atom or group of atoms.
Describe the ions in table salt.
Na^+ is a sodium atom that has lost an electron. Chemists call this a sodium ion. (it’s + because electrons are negatively charged)
Cl^- is a chlorine atom that has gained an electron. Chemists call this a chloride ion. (it’s - because it has one extra electron
How can we tell there must be a strong attraction between positive and negative ions?
Sodium chloride has a very high melting point.
What is an ionic bond? (DEFINITIONNNNNNN)
An ionic bond is the force of attraction between positive and negative ions in a compound
Give two examples of ionic compounds
- Sodium chloride (NaCl)
- Magnesium oxide (MgO)
- see pages 223 + 224 of textbook for more information and diagrams about these - study and learn it!*
Give the four general properties of ionic compounds
- they’re usually solid at room temperature
- they usually have high melting and boiling points
- they usually dissolve in water
- they usually conduct electricity when molten (melted) or when dissolved in water
- see pages 224 & 225 of textbook for more information and diagrams about these - study and learn it!*
Give the four general properties of covalent compounds
- they’re usually either a liquid or a gas at room temperature
- they usually have low melting and boiling points
- many (but not all) of them don’t dissolve in water
- they don’t conduct electricity
List the 5 summarised properties of ionic and covalent compounds
Ionic - consist of positive and negative ions - usually solid at room temperature - usually high melting and boiling points - usually soluble in water - conduct electricity when melted/dissolved in water Covalent - usually consist of individual molecules - usually liquid/gas at room temperature - usually low melting points - usually insoluble in water - do not conduct electricity
