4.1 Development of the Periodic Table of Elements

Short Answer Questions

1. Who was one of the early scientists involved in the development of the periodic table?
   Answer
   Lavoisier, Döbereiner, Newlands, Meyer, Mendeleev, or Moseley.
2. According to the modern periodic table, how are elements ordered?
   Answer
   By increasing atomic number (proton number).
3. What are the vertical columns in the periodic table called?
   Answer
   Groups.
4. What are the horizontal rows in the periodic table called?
   Answer
   Periods or Series.
5. What determines the number of the group an element is in?
   Answer
   The number of valence electrons.
6. What is the name given to elements in Group 1?
   Answer
   Alkali metals.
7. What is the name given to elements in Group 18?
   Answer
   Noble gases or inert gases.
8. What is the general term for elements that have properties of both metals and non-metals?
   Answer
   Metalloids or semi-metals.
9. What is the term for elements in the periodic table that are located between Group 2 and Group 13?
   Answer
   Transition elements.
10. What is the group that contains the halogens?
    Answer
    Group 17.
11. What is the name for elements with only one atom per molecule?
    Answer
    Monatomic gases.
12. How many valence electrons does an atom from Group 1 have?
    Answer
    1.
13. How many valence electrons does an atom from Group 17 have?
    Answer
    7.
14. What is the term for atoms that are chemically stable due to having a full outer shell of electrons?
    Answer
    Noble gases or inert gases (they have a full duet or octet).
15. What is the most reactive group of metals?
    Answer
    Group 1, the alkali metals.
16. What is the most reactive group of non-metals?
    Answer
    Group 17, the halogens.
17. What happens to the atomic size of elements going down a group?
    Answer
    The atomic size increases.
18. What happens to the atomic size of elements from left to right across a period?
    Answer
    The atomic size decreases.
19. What is the trend for metallic character across a period?
    Answer
    Metallic character decreases from left to right across a period.
20. What is the trend for reactivity in Group 1?
    Answer
    Reactivity increases going down the group.

Explanation Questions

1. Explain how the elements in the modern periodic table are arranged, and why this arrangement is useful.
   Answer
   Elements are arranged by increasing atomic number, which corresponds to the number of protons in the nucleus. This arrangement is useful because it groups elements with similar chemical properties together, due to the recurring pattern of electronic structure, thus allowing for prediction of properties and reactions.
2. Describe the concept of valence electrons and how they relate to the group number of an element.
   Answer
   Valence electrons are the electrons in the outermost shell of an atom. The number of valence electrons determines the group number for main group elements. For example, elements in Group 1 have 1 valence electron, Group 2 have 2, and so on. These electrons are involved in chemical bonding, and thus influence chemical properties.
3. Explain the meaning of the term ‘monatomic gas’ and give an example.
   Answer
   A monatomic gas is a gas that exists as single atoms rather than as molecules. An example of a monatomic gas is helium (He) or neon (Ne), which are noble gases in Group 18.
4. What is the ‘octet rule’ and why is it important for understanding the chemical properties of elements?
   Answer
   The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full outer shell of eight electrons (or two for elements like hydrogen and helium). This rule is important because it explains why atoms form chemical bonds and how they achieve stability, which in turn determines their chemical properties.
5. Explain why Group 1 metals are so reactive, and how their reactivity changes down the group.
   Answer
   Group 1 metals are highly reactive because they have only one valence electron that is easily lost to form a positive ion. The reactivity increases going down the group because the outermost electron is further from the nucleus and is more easily lost.
6. Explain why Group 17 non-metals are so reactive, and how their reactivity changes down the group.
   Answer
   Group 17 non-metals (halogens) are highly reactive because they have seven valence electrons and readily gain one electron to achieve a stable octet. The reactivity decreases going down the group because the outermost electrons are further from the nucleus, making it harder to attract another electron.
7. What are transition elements and what are some of their typical properties?
   Answer
   Transition elements are located in the d-block of the periodic table, between Group 2 and Group 13. They typically have variable oxidation states, form coloured compounds, and can act as catalysts. Many are good conductors of electricity and heat.
8. What are metalloids and what is their main characteristic?
   Answer
   Metalloids, also known as semi-metals, are elements that have properties of both metals and non-metals. Their main characteristic is their semiconductivity, meaning that they conduct electricity better than non-metals but not as well as metals.
9. Explain how the atomic radius of elements changes both across a period and down a group and why.
   Answer
   The atomic radius decreases across a period from left to right because the number of protons increases, resulting in a stronger attraction between the nucleus and the electrons. The atomic radius increases down a group because new electron shells are added, which increase the distance of the outer electrons from the nucleus.
10. Describe how the properties of oxides change across a period in the periodic table and why.
    Answer
    The properties of oxides change across a period from basic (left) to acidic (right). For example, Group 1 oxides such as sodium oxide are basic, while Group 17 oxides like chlorine oxides are acidic. Oxides in the middle of the period can be amphoteric (both acidic and basic), such as aluminum oxide. This change is due to the change in metallic character of the elements in the period.