The periodic table

In a jeweler'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 soda).

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 lowercase 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?

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 aluminum 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 an everyday use.

Solar panels and computer processors contain silicon.

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

A cell 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, nonmetal, or metalloid.
2. b) Choose two of them and justify, using their properties, why they are used in that part of the cell 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 nonmetals.
2. b) Describe the trend observed: how does metallic character change moving from left to right across a row of the table?

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) Explain 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.

Helium, neon, and argon are part of 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 periodic 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 nonmetal?
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 periodic table does hydrogen belong to: noble gases or a different one? What about helium?
2. b) Using the families of the periodic table, explain why helium is much safer than hydrogen for this use, even though it is more expensive.

An unknown element is a colorless 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 an everyday use for one of them and relate it to its properties.

In the lab, dropping a small piece of lithium into water makes it bubble gently; sodium moves quickly across the surface of the water, and potassium even produces sparks. All three are in the same column of the periodic 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 it is dropped into water, and justify your answer.