The periodic table
A pure gold ring and a glass of distilled water are both pure substances. But if you could see their particles through a magic magnifying glass, you would see something very different: in gold all the atoms are the same; in water, each particle is made of two types of atom joined together.
Elements and compounds
If you pass an electric current through liquid water, you get two different gases (hydrogen and oxygen), but however much heat or electricity you apply to pure oxygen gas, you will never get a simpler substance: why can some pure substances be broken down into others while others cannot?
In a jeweller's shop they work with pure gold, and in the laboratory we have pure distilled water. However, gold is an element and water is a compound. The figure shows…
In a jeweller's shop they work with pure gold, and in the laboratory we have pure distilled water. However, gold is an element and water is a compound. The figure shows their particle models.
Explain in your own words the difference between an element and a compound.
Classify these substances as element or compound: $\text{O}2$ (oxygen in the air), $\text{H}2\text{O}$ (water), $\text{Fe}$ (iron in a nail), $\text{NaCl}$ (table salt)…
Classify these substances as element or compound: $\text{O}_2$ (oxygen in the air), $\text{H}_2\text{O}$ (water), $\text{Fe}$ (iron in a nail), $\text{NaCl}$ (table salt) and $\text{CO}_2$ (gas in soft drinks).
Chemical symbols
Writing "hierro" or "iron" every time you want to name an element would be very slow, and each language would also use a different word. That is why chemists use symbols that are the same all over the world.
Write the chemical symbol for these elements: hydrogen, oxygen, carbon, nitrogen and calcium.
Write the chemical symbol for these elements: hydrogen, oxygen, carbon, nitrogen and calcium.
Which element does each of these symbols represent? $\text{He}$, $\text{Li}$, $\text{Mg}$, $\text{P}$ and $\text{S}$.
Which element does each of these symbols represent? $\text{He}$, $\text{Li}$, $\text{Mg}$, $\text{P}$ and $\text{S}$.
Cobalt is written $\text{Co}$ and carbon monoxide is written $\text{CO}$. Although they use the same letters, one is an element and the other is a compound. Explain the…
Cobalt is written $\text{Co}$ and carbon monoxide is written $\text{CO}$. Although they use the same letters, one is an element and the other is a compound. Explain the rule for writing chemical symbols and why capital and lower-case letters must be respected.
How the table is organised: groups and periods
The periodic table does not place the elements at random: it orders them by their atomic number $Z$, and arranges them so that elements that behave similarly end up together.
Tap different elements in the interactive table and see how the group and period change. Notice that hydrogen (H) and helium (He) are in the same period, but in very different groups.
In the periodic table, elements are not arranged at random. What are the columns called? And the rows? What do elements in the same column have in common?
In the periodic table, elements are not arranged at random. What are the columns called? And the rows? What do elements in the same column have in common?
Look up magnesium ($\text{Mg}$) in the periodic table. The figure shows what an element's cell looks like. a) What is its atomic number? b) In which period (row) and…
Look up magnesium ($\text{Mg}$) in the periodic table. The figure shows what an element's cell looks like.
- a) What is its atomic number?
- b) In which period (row) and which group (column) is it located?
- c) Name another element in the same group and state what the two will have in common.
Metals, non-metals and metalloids
If you hit an iron nail with a hammer it bends without breaking, whereas a lump of coal crumbles to powder at once and a slice of silicon shatters like glass: what causes such radical differences between elements that are solid at room temperature?
Frying pans, electrical cables and pipes are usually made of metals such as aluminium or copper. Name three typical properties of metals and relate them to these uses.
Frying pans, electrical cables and pipes are usually made of metals such as aluminium or copper. Name three typical properties of metals and relate them to these uses.
Element A is a shiny solid that conducts electricity very well. Element B is a yellowish gas that does not conduct it. a) Which of the two is a metal and which is a…
Element A is a shiny solid that conducts electricity very well. Element B is a yellowish gas that does not conduct it.
- a) Which of the two is a metal and which is a non-metal? Justify your answer.
- b) Give a possible example of an element for each case and a daily use.
Solar panels and computer processors contain silicon. a) What is a metalloid? b) Explain why silicon, due to its intermediate behaviour between metals and non-metals, is…
Solar panels and computer processors contain silicon.
- a) What is a metalloid?
- b) Explain why silicon, due to its intermediate behaviour between metals and non-metals, is used to manufacture chips.
Important families
Some groups have their own name because their elements share a very characteristic behaviour.
Helium, neon and argon form the noble gas family. What chemical property do they all share? Why do you think they are called "noble"?
Helium, neon and argon form the noble gas family. What chemical property do they all share? Why do you think they are called "noble"?
In fireworks, lithium salts produce red sparks, sodium salts yellow sparks, and potassium salts lilac sparks. These three elements are in the first column of the…
In fireworks, lithium salts produce red sparks, sodium salts yellow sparks, and potassium salts lilac sparks. These three elements are in the first column of the periodic table. The figure shows the column of the table where they are located.
- a) What is the name of the family to which they belong?
- b) Name one property shared by these metals.
The chlorine that disinfects swimming pool water and the fluorine in some toothpastes are in the same column of the table, group $17$. a) What is the name of this…
The chlorine that disinfects swimming pool water and the fluorine in some toothpastes are in the same column of the table, group $17$.
- a) What is the name of this family?
- b) Name one property shared by its elements.
Back to the start: The gold ring is an element because it only contains identical gold atoms ($\text{Au}$), whereas water is a compound ($\text{H}_2\text{O}$) because it brings together atoms of two different elements bonded in the same proportion every time.