Question

extension: the periodic table
get the gizmo ready:

• create a neutral hydrogen atom.
• if you have access to a periodic table, open it now. (not required.)

question: the 117 or so known elements are arranged in the periodic table. why does the periodic table have the shape it has?

1. form a hypothesis: look at the first three rows of the periodic table below.

why do you think the elements are arranged the way that they are?

1. draw diagrams: create an electron - dot diagram for each of the elements below. use the gizmo to help you do this. to check your work, turn on show electron dot diagram.

h he
li be b c n o f ne
na mg al si p s cl ar

1. analyze: what do the elements in each column of the periodic table have in common?
2. draw conclusions: how is the periodic table organized?

Explanation:

1. The elements in the periodic table are arranged by increasing atomic number. This arrangement shows trends in chemical and physical properties. For example, elements in the same column (group) have the same number of valence electrons, which gives them similar chemical reactivity.
2. Electron - dot diagrams represent the valence electrons of an atom. For hydrogen (H), it has 1 valence electron, so the electron - dot diagram has 1 dot. Helium (He) has 2 valence electrons, so it has 2 dots. Lithium (Li) has 1 valence electron, beryllium (Be) has 2, boron (B) has 3, carbon (C) has 4, nitrogen (N) has 5, oxygen (O) has 6, fluorine (F) has 7, and neon (Ne) has 8. Sodium (Na) has 1, magnesium (Mg) has 2, aluminum (Al) has 3, silicon (Si) has 4, phosphorus (P) has 5, sulfur (S) has 6, chlorine (Cl) has 7, and argon (Ar) has 8.
3. Elements in each column (group) of the periodic table have the same number of valence electrons. This leads to similar chemical behavior as the valence electrons are involved in chemical bonding.
4. The periodic table is organized by increasing atomic number. It is divided into periods (rows) and groups (columns). Elements in the same period have the same number of electron shells, and elements in the same group have the same number of valence electrons.

Answer:

1. The elements are arranged by increasing atomic number, which shows trends in their properties.
2. H: 1 dot; He: 2 dots; Li: 1 dot; Be: 2 dots; B: 3 dots; C: 4 dots; N: 5 dots; O: 6 dots; F: 7 dots; Ne: 8 dots; Na: 1 dot; Mg: 2 dots; Al: 3 dots; Si: 4 dots; P: 5 dots; S: 6 dots; Cl: 7 dots; Ar: 8 dots.
3. They have the same number of valence electrons.
4. It is organized by increasing atomic number, with periods (rows) and groups (columns), where elements in the same period have the same number of electron shells and elements in the same group have the same number of valence electrons.