The periodic table

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) and $\text{CO}_2$ (gas in soft drinks).

Glucose has the formula $\text{C}_6\text{H}_{12}\text{O}_6$ and ozone has the formula $\text{O}_3$.

1. a) Which of the two is an element and which is a compound?
2. b) Justify your answer by counting the types of atoms that form each formula.

Water is a pure substance, just like oxygen, yet only oxygen is an element.

The apparatus for part b) is shown in the figure.

1. a) Reason why water cannot be an element by considering the types of atoms that form it.
2. b) Passing electric current through water decomposes it. Which two elements are obtained? Explain what this experiment shows about the nature of water.

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 $\text{S}$.

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.

Some symbols do not resemble the name of the element: iron is $\text{Fe}$, gold $\text{Au}$, silver $\text{Ag}$ and sodium $\text{Na}$.

1. a) Which ancient language do these symbols come from?
2. b) Match each symbol with its original name: ferrum, aurum, argentum and natrium.

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?

Carbon has atomic number $6$ and oxygen has atomic number $8$. The figure shows the model of an atom.

1. a) Explain what the atomic number is.
2. b) How many protons does a carbon atom have? And an oxygen atom?
3. c) If the atoms are neutral, how many electrons does each one have?

Look up magnesium ($\text{Mg}$) in the periodic table. The figure shows what an element's cell looks like.

1. a) What is its atomic number?
2. b) In which period (row) and which group (column) is it located?
3. c) Name another element in the same group and state what the two will have in common.

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.

1. a) Which of the two is a metal and which is a non-metal? Justify your answer.
2. b) Give a possible example of an element for each case and a daily use.

Solar panels and computer processors contain silicon.

1. a) What is a metalloid?
2. b) Explain why silicon, due to its intermediate behaviour between metals and non-metals, is used to manufacture chips.

A mobile phone contains copper in the internal wires, lithium in the battery, silicon in the processor, and carbon and hydrogen in the plastic casing.

1. a) Classify copper, lithium, silicon and carbon as metal, non-metal or metalloid.
2. b) Choose two of them and justify, using their properties, why they are used in that part of the mobile phone.

In period $2$ of the periodic table, the elements are, in this order: $\text{Li}$, $\text{Be}$, $\text{B}$, $\text{C}$, $\text{N}$, $\text{O}$, $\text{F}$ and $\text{Ne}$.

1. a) Classify these eight elements as metals, metalloids and non-metals.
2. b) Describe the trend observed: how does metallic character change moving from left to right across a row of the table?

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 periodic table. The figure shows the column of the table where they are located.

1. a) What is the name of the family to which they belong?
2. 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 $17$.

1. a) What is the name of this family?
2. b) Name one property shared by its elements.

Francium ($\text{Fr}$) is in the first column of the periodic table, below lithium, sodium and potassium. Without knowing anything else about it, predict:

1. a) Will it be a metal or a non-metal?
2. b) Will it react easily with water?
3. c) Will it be a soft or hard metal?

Justify each prediction using the position of francium in the table.

The airship Hindenburg, in $1937$, was filled with hydrogen to fly and caught fire in a few seconds. Today weather balloons are filled with helium.

1. a) Which family of the table does hydrogen belong to: noble gases or a different one? What about helium?
2. b) Using the families of the table, explain why helium is much safer than hydrogen for this use, even though it is more expensive.

An unknown element is a colourless gas that does not react with any other substance and is located in the last column of the periodic table.

1. a) Which family does it belong to?
2. b) Name two elements that it could be.
3. c) Give a daily use for one of them and relate it to its properties.

In the laboratory, dropping a small piece of lithium into water bubbles gently; sodium moves quickly across the surface of the water, and potassium even produces sparks. All three are in the same column of the table, one below the other.

1. a) What pattern does the reactivity of these metals follow going down the group?
2. b) Rubidium is below potassium. Predict what will happen when dropping it into water and justify your answer.

Neon glows in illuminated signs and argon fills the inside of many light bulbs. Both are in the same group of the table. Furthermore, we know that elements in the same group have the same number of electrons in their outermost shell. The figure shows their atomic models.

1. a) What property do neon and argon share by being in the same group?
2. b) Use the information about electrons in the outer shell to explain why elements in the same group have such similar properties.