Visualising reaction mechanisms in VCE Chemistry can sometimes be difficult. Making plastic models helps, but I’ve been thinking that it would be much more convenient if students had their own paper version of molecular models that they could keep for themselves and use at home.

That’s why I created Foldable Biomolecules. Each Foldable Biomolecule is a PDF template that students can fold into a shape that demonstrates a chemical reaction clearly. Pull apart the edges of each sheet to visualise a hydrolysis reaction, and push them back together to visualise a condensation reaction.

These paper-based biomolecules are downloadable, shareable and much quicker to set up than their plastic counterparts.

You can also download the complete set of Foldable Biomolecules as a single PDF here.

Significant figures tell you how accurately a number is known. This invariably depends on the precision of your instruments.

To illustrate this, use a pencil and a ruler to draw a square with sides of 8.109435 cm in length. Now, calculate the area of the square that you’ve drawn.

A ruler can only measure length to within ±0.1 cm. Our square therefore has sides 8.1 cm in length (not 8.109435 cm) because our measurements are limited by the accuracy of the ruler. The area of our square is therefore 8.1×8.1=66 cm², not 65.762936019225 cm², because there was no way to measure all of those decimal places precisely using a ruler.

Accurately-known digits are known as significant digits. All other digits are described as not significant. We must always round our final answer (not the intermediate steps) to the correct number of significant digits by following the six rules below.

1. Numbers without a decimal point

First non-zero digit is significant

Last non-zero digit is significant

All digits in-between are significant

45 is to 2 significant figures (s.f.)

1,240 (3 s.f.)

68,686,000 (5 s.f.)

2. Numbers with a decimal point

First non-zero digit is significant

All digits afterwards are significant

1.2 (2 s.f.)

6.810 (4 s.f.)

900,001 (6 s.f.)

3. Scientific notation

Scientific notation is a way of writing numbers in the form:

a × 10^{b } where 1 ≤ a < 10.

Count the number of significant figures in a to find the number of significant figures in the number (a × 10^{b}).

5.56 × 10^{3} is to 3 significant figures

2.012 × 10^{-4} is to 4 significant figures

4. Conversions

Some unit conversions are exact and are said to have an unlimited number of significant figures.

1 minute = 60.0000000000… seconds (infinite s.f.)

1 metre = 100.0000000000… metres (infinite s.f.)

Temperatures usually have 3 (sometimes 4) significant figures when converted into Kelvin!

10°C = 283 K (3 significant figures)

100°C = 373 K (3 significant figures)

4000°C = 4273 K (4 significant figures)

5. Addition and subtraction

Rule: Always round your final answer (not any intermediate answers!) to the smallest number of decimal places.

441 + 65.42 = 506 (use zero decimal places)

200.1 – 144.2456 = 55.9 (use 1 decimal place)

6. Multiplication and division

Rule: Always round your answer so it has the same number of significant figures as the input value with the smallest number of significant figures.

481.56 × 14.5 = 6980 (use only 3 s.f.)

7800 ÷ 41.1 = 190 (use only 2 s.f.)

Remember to round your ANSWER (not the intermediate steps) to the correct number of significant figures.

Questions? Comments? Still confused? Leave a message in the comments below. I’ve tried to make sig figs as simple as I can in this post.

It’s so much easier to change your teaching style at the beginning of a year than in the middle. This is because new students in a new class after a long summer break are much more receptive to change than the ones who are already used to the way you teach. In fact, most students return from their summer vacation eagerly expecting something new!

The following checklist is based on what I’ve learned since I started teaching in September 2006; and I believe it’s a great way to start teaching a new class.

Part A: Get to know your students

1. Make a grades database in Excel

Start with the following columns: Surname, First name, Email address and Gender.

Make columns for any compulsory assessment tasks (raw score and percentage). If any assessment tasks are submitted late, just add a comment to the relevant cell in the spreadsheet. Nothing more needs to be recorded in this database. Keep it really simple!

2. Set up group email lists

Use your email client (e.g. Outlook) to create groups for (a) your students and (b) your students’ parents. You’ll use these to distribute resources and reminders in future.

3. Email the parents

Send an introductory email to the parents and attach the course outline. For most students, this will be the only time you ever email their parents. Just send them one message to establish contact at the start of the year, and they’ll feel welcome to email you if they have any concerns regarding their child’s progress in your subject. Remember to put their addresses in the bcc field to hide their addresses from each other!

4. Prepare start-up packs for your students

See next week’s post on creating start-up packs for VCE Chemistry students, or make a similar start-up pack for the students in your subject.

5. Put students’ birthdays into your calendar

Take the time to put all your students’ birthdays into your calendar at the start of the year, then wish them a happy birthday face-to-face on the day. This builds rapport, and students really appreciate it!

Part B: Get to know your curriculum

6. Read and annotate all your textbooks

Teachers need to be very familiar with allthe resources they give their students. Just as you’d pre-watch a YouTube video before you show it to the class, you also need to pre-read the textbook before you endorse it and use it in class.

Unless you’re already done so, read all the textbooks for all the subjects you’ll be teaching from cover to cover. Make notes in the margins as you would expect your students to do. Highlight important facts carefully and summarise every paragraph all the difficult sections in your own words. These will be the words that you write on the whiteboard (along with any important diagrams) during the lesson.

Your school will give you a plan for the course you’re going to teach. However, these plans don’t always contain all the information you need. Get a copy of your course plan and add the following columns to it:

Textbook chapter references for each week

Any extra resources you want to use (e.g. YouTube videos) – you can always use more later; add them to the course plan if you do.

Assignments / tests and their due dates. Give each assignment/test a name and stick to it. Label how much each assignment/test counts towards the student’s final grade.

Experiments. Label how long each experiment takes and plan which days to do each of them for the entire term in advance.

8. Gather misconceptions for each topic

Dialogues about misconceptions are a brilliant way to introduce new Chemistry topics. Derek Muller, founder of the YouTube channel Veritasium, explains this beautifully.

Using your own experience marking tests and examinations, annotate your own textbook with misconceptions that students have about each topic. For example:

9. Find out what’s going to be on the tests and exam!

Not all schools teach all topics on the curriculum, and not all schools test all the topics in the examination. Find out the topics to be tested on the tests and examinations and tell the students in advance (with textbook chapter references) so they can plan their revision.

Part C: The first few lessons

10. Monthly Seating Plans

Allow the students to choose their own seats in the first lesson. Sketch a map of the room so that during the introduction session, you can label who chooses to sit where. Tell the students that you will modify the seating plan every calendar month to break up students who don’t work productively together.

Be very strict about maintaining the seating plan. This creates an atmosphere of order, structure, fairness and respect very early in the year. Be strict about punctuality and homework as well.

11. Introduction lesson

Stand in a circle: “What’s your name” and “tell me something interesting about you”

Ask around the circle again: “What is [Chemistry/Physics/History]?

Sit down. Teacher answers questions 1 and 2 for the class. Distribute the start-up packs and show their contents.

Show students the textbook and get them to write their names in it. Don’t be afraid to write in your textbook!

Revisionof fundamental concepts from last year (a worksheet). Use this to recap the required knowledge for this course.

Dictate classroom rules & homework expectations into students’ notebooks

Show the students your office

Homework is to make a name plate to put on your desk (be strict about this)

How to take great notes (see my post on this in November 2014)

Start teaching the theory behind first topic to be learned. Follow textbook closely.

13. Third lesson (experiment/demo)

Do the first week’s experiment in the third lesson if possible. For year 11, doing flame tests in watch glasses is a great place to start. Keep the students motivated by questioning every aspect of the experiment: why use methanol, not ethanol? (Try both!) Why does methanol emit light when it combusts? (Electrons absorb energy/emit quanta of light) Why does the presence of metals change the colour of the flame? (Electrons at different energy levels in different elements emit light with different wavelengths when falling back to their ground state, producing different colours).

14. Do a feedback survey

Use SurveyMonkey to set up a very simple, anonymous survey and send it via group email to your students on Friday afternoon. There should be very few questions:

Which class are you in? (Tick-boxes)

How would you rate Chemistry lessons so far? (1-5 rating)

(Any other questions you want to ask)

Is there anything you particularly (dis)like about your Chemistry lessons so far? (Large comment box)

Thank the students for their honest feedback on Monday. Honest feedback builds rapport!

15. Plagiarism & Referencing Session (optional)

To establish an honest work ethic in the classroom, you can give your students a one-off session on Plagiarism & Referencing. Use PowerPoint such as these and give all students a printed handout. The purpose of this session is merely to raise awareness that copying is detrimental to student learning and should include:

what plagiarism is (and why it hinders learning);

the severe punishments for plagiarism in academia and in industry;

how to locate good learning resources (with emphasis on the textbook!); and

how to reference those resources in an assignment (using Harvard or APA style).

In some schools, the library staff are happy to arrange (and teach!) these sessions for you. Arrange this Plagiarism & Referencing session early in your course if you think that copying and cheating is a widespread problem in your class. ■

Is there anything I’ve missed out? Write in the comments section below.