Question

dmitri mendeleev:

• arranged elements by __________ ________ __________.
• predicted __________ of missing __________.

henry moseley:

• discovered that each __________ has a unique ________ __________.
• arranged elements by __________ ________ __________.
• now all elements fit into place based on properties

modern periodic law:
properties of elements __________ when elements are arranged by ________ ________ __________.
questions about the extended periodic table:
why do you think these elements get pulled out?
which element is in a different column than we are used to?
what happens to the number of the energy level as you begin each new row?
what is the similar characteristic in each column?

Explanation:

Dmitri Mendeleev:

• arranged elements by increasing atomic mass.
• predicted properties of missing elements.

Henry Moseley:

• discovered that each element has a unique atomic number.
• arranged elements by increasing atomic number.
• now all elements fit into place based on properties

Modern Periodic Law:

Properties of elements repeat periodically when elements are arranged by increasing atomic number.

Questions about the extended periodic table:

1. Why do you think these elements get pulled out?

Elements like lanthanides and actinides (inner transition metals) are pulled out because their electron configurations involve filling inner f - orbitals. This leads to similar chemical properties among them, and separating them makes the periodic table more compact and easier to read, as their main - group - like periodic trends are less prominent compared to the s, p, and d - block elements.

1. Which element is in a different column than we are used to?

Hydrogen is often considered to be in a different column than we might intuitively place it. It has one valence electron like the alkali metals (group 1), but it is also a non - metal and can form bonds similar to halogens in some cases, so its placement (usually above group 1 but with unique properties) makes it seem out of the "usual" column for its type.

1. What happens to the number of the energy level as you begin each new row?

When you begin each new row (period) in the periodic table, the principal energy level (n) of the outermost electrons increases by 1. For example, in period 1, the outermost electrons are in the n = 1 energy level; in period 2, they are in the n = 2 energy level, and so on.

1. What is the similar characteristic in each column?

In each column (group) of the periodic table, elements have the same number of valence electrons. This similar number of valence electrons leads to similar chemical properties, such as similar reactivity patterns (e.g., group 1 elements all have 1 valence electron and are highly reactive metals, group 17 elements all have 7 valence electrons and are highly reactive non - metals).

Answer:

Dmitri Mendeleev:

• arranged elements by increasing atomic mass.
• predicted properties of missing elements.

Henry Moseley:

• discovered that each element has a unique atomic number.
• arranged elements by increasing atomic number.
• now all elements fit into place based on properties

Modern Periodic Law:

Properties of elements repeat periodically when elements are arranged by increasing atomic number.

Questions about the extended periodic table:

1. Why do you think these elements get pulled out?

Elements like lanthanides and actinides (inner transition metals) are pulled out because their electron configurations involve filling inner f - orbitals. This leads to similar chemical properties among them, and separating them makes the periodic table more compact and easier to read, as their main - group - like periodic trends are less prominent compared to the s, p, and d - block elements.

1. Which element is in a different column than we are used to?

Hydrogen is often considered to be in a different column than we might intuitively place it. It has one valence electron like the alkali metals (group 1), but it is also a non - metal and can form bonds similar to halogens in some cases, so its placement (usually above group 1 but with unique properties) makes it seem out of the "usual" column for its type.

1. What happens to the number of the energy level as you begin each new row?

When you begin each new row (period) in the periodic table, the principal energy level (n) of the outermost electrons increases by 1. For example, in period 1, the outermost electrons are in the n = 1 energy level; in period 2, they are in the n = 2 energy level, and so on.

1. What is the similar characteristic in each column?

In each column (group) of the periodic table, elements have the same number of valence electrons. This similar number of valence electrons leads to similar chemical properties, such as similar reactivity patterns (e.g., group 1 elements all have 1 valence electron and are highly reactive metals, group 17 elements all have 7 valence electrons and are highly reactive non - metals).