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Learn to draw visual representations of molecules using dots and lines.
Why do some atoms stick together like powerful magnets while others drift apart? The secret lies in a 'hidden handshake' of electrons that you can map out on a simple piece of paper.
To understand how atoms bond, we only care about their valence electrons—the electrons in the outermost shell. Think of these as the 'arms' an atom uses to grab onto others. For most atoms, the goal is to reach the Octet Rule, which means having electrons to become stable (like the Noble Gases). To draw a Lewis symbol, we write the element's chemical symbol and place dots around it to represent these valence electrons. We place one dot on each of the four sides (top, bottom, left, right) before pairing them up.
1. Identify the group: Nitrogen is in Group 15, so it has valence electrons. 2. Place dots: Put one dot on each side (4 dots). 3. Pair up: Place the dot on the top to create one pair and three 'lonely' electrons. 4. Result: with one pair and three single dots.
Quick Check
How many valence dots would you draw for an Oxygen atom (Group 16)?
Answer
6 dots (two pairs and two single electrons).
When two atoms share a pair of electrons, they form a covalent bond. In a Lewis structure, we represent this shared pair as a single solid line. The central atom is usually the one that needs the most electrons to reach its octet. For example, in Methane (), Carbon has valence electrons and needs more. Each Hydrogen has and needs more (Hydrogen is an exception; it only needs total). By sharing, everyone wins!
1. Count total valence electrons: total. 2. Place the central atom: Oxygen goes in the middle because it needs more bonds. 3. Draw single bonds: Connect each to with a line (). Each line uses electrons. 4. Distribute remaining electrons: We used electrons for bonds. Place the remaining as 'lone pairs' on the Oxygen. 5. Check: Oxygen now has electrons (4 from bonds + 4 lone), and each Hydrogen has .
Quick Check
In a Lewis structure, what does a single solid line represent?
Answer
One shared pair of electrons (2 electrons total).
Sometimes, sharing one pair isn't enough to satisfy the Octet Rule. If atoms are still 'hungry' for electrons, they may share two or even three pairs. A double bond is shown as two parallel lines () and represents shared electrons. A triple bond is shown as three lines () and represents shared electrons. These bonds are much stronger and shorter than single bonds. Nitrogen gas () is a classic example where two atoms must share three pairs to both reach electrons.
1. Total electrons: . 2. Layout: . 3. Initial bonds: Using single bonds uses electrons, leaving . If we give its octets, is left with only electrons. 4. Shift to double bonds: Move a lone pair from each Oxygen to the bonding area. 5. Final Structure: . Now Carbon has electrons (from 4 bonds) and each Oxygen has (4 from bonds + 4 lone).
How many total valence electrons are in a molecule of Ammonia ()?
Which atom is most likely to be the central atom in a molecule?
A triple bond involves the sharing of 3 total electrons.
Review Tomorrow
Tomorrow morning, try to draw the Lewis dot symbol for Chlorine and Carbon from memory.
Practice Activity
Try drawing the Lewis structure for . Hint: It requires a double bond to satisfy the octet rule for both atoms!