Chemistry
KEY CONCEPT Sizes of particles and orders of magnitude
KEY WORDS magnitude diameter radius nanometre
Learning objectives: • • •
identify the scale of measurements of length explain the conversion of small lengths to metres explain the relative sizes of electrons, nuclei and atoms.
Let’s start with the particles we can see. A grain of sand and a grain of sugar are about the same size and are made of crystals. These crystals are made up of much smaller sections that we cannot see.
Orders of magnitude Placing a tennis ball, golf ball, basketball and table tennis ball in order of size is easy. unit
basketball
tennis ball
golf ball
table tennis ball
cm
25.0
6.8
4.1
0.4
m
0.25
0.068
0.041
0.004
We can measure objects smaller than these in millimetres.
Figure 2.51 It is easy to put these in order of diameter.
1 m = 1000 mm 1 mm = 0.001 m or 1 mm = 10–3 m We can even see objects in the next set of smaller units, the micrometre. We measure the width of a human hair in this unit. 1 m = 1 000 000 μm 1 μm = 0.000001 m or 1 μm = 10 –6 m After that we need instruments to help us see and measure lengths. We have discussed carbon nanotubes and graphene as a monolayer of carbon atoms. Later, we will discuss large molecules such as DNA. These next sets of objects are in the ‘nano-scale.’ The unit is the nanometre. 1 m = 1 000 000 000 nm 1 nm = 0.000000001 m or 1 nm = 10 –9 m 1
Calculate the number of basketballs it would take to make a kilometre.
MATHS
2
A carbon nanotube has a length of 2 × 10 –9 m. Calculate the number of nanotubes that would fit in 1 mm.
1 cm = 0.01 m is the long way to write the conversion.
Atoms and ions Going one step further down into the atomic scale: • the radius of an atom is measured in picometres (pm), 10 –12 m
84
1 cm = 10 –2 m is the conversion into standard form.
AQA GCSE Chemistry for Combined Science: Trilogy: Student Book
75054_P054_091.indd 84
5/24/16 8:53 PM