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:

To solve the fill - in - the - blanks related to the periodic table and the work of scientists, we use our knowledge of the history and principles of the periodic table:

Dmitri Mendeleev

• Mendeleev is famous for arranging the elements in the periodic table in the order of increasing atomic mass. He also predicted the properties of the missing elements. So the blanks are: arranged elements by $\boldsymbol{\text{increasing atomic mass}}$; predicted $\boldsymbol{\text{properties}}$ of missing $\boldsymbol{\text{elements}}$.

Henry Moseley

• Moseley discovered that each element has a unique atomic number. And he arranged the elements in the periodic table in the order of increasing atomic number. So the blanks are: discovered that each $\boldsymbol{\text{element}}$ has a unique $\boldsymbol{\text{atomic number}}$; arranged elements by $\boldsymbol{\text{increasing atomic number}}$.

Modern Periodic Law

• The modern periodic law states that the properties of elements repeat (or show periodicity) when elements are arranged by increasing atomic number. So the blanks are: Properties of elements $\boldsymbol{\text{repeat (periodically)}}$ when elements are arranged by $\boldsymbol{\text{increasing atomic number}}$.

Answer:

s for the fill - in - the - blanks:

Dmitri Mendeleev:

• arranged elements by $\boldsymbol{\text{increasing atomic mass}}$.
• predicted $\boldsymbol{\text{properties}}$ of missing $\boldsymbol{\text{elements}}$.

Henry Moseley:

• discovered that each $\boldsymbol{\text{element}}$ has a unique $\boldsymbol{\text{atomic number}}$.
• arranged elements by $\boldsymbol{\text{increasing atomic number}}$.

Modern Periodic Law:

Properties of elements $\boldsymbol{\text{repeat (periodically)}}$ when elements are arranged by $\boldsymbol{\text{increasing atomic number}}$.

For the questions about the extended periodic table:

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

Elements like the lanthanides and actinides (the inner - transition metals) have very similar chemical properties because they have similar electron configurations (the filling of the f - orbitals). To make the periodic table more organized and to show the periodicity of properties more clearly, these elements (which have similar properties within their groups) are pulled out and placed in separate rows at the bottom of the periodic table.

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

Hydrogen is an element that is often considered to be in a different column than we might expect. Hydrogen has only 1 valence electron, similar to the alkali metals (Group 1), but it is also a non - metal and has some properties similar to halogens (Group 17) in terms of its ability to form diatomic molecules and react with metals and non - metals. So it is sometimes placed separately or its position is a subject of discussion as it doesn't fully fit the typical properties of either Group 1 or Group 17.

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

As we begin each new row (period) in the periodic table, the number of the energy level (the principal quantum number, $n$) increases by 1. For example, in the first period, the energy level $n = 1$, in the second period $n=2$, and so on.

4. What is the similar characteristic in each column?

In each column (group) of the periodic table, the elements have the same number of valence electrons. And because of the same number of valence electrons, they have similar chemical properties. For example, all the elements in Group 1 (alkali metals) have 1 valence electron and are highly reactive metals, while all the elements in Group 17 (halogens) have 7 valence electrons and are highly reactive non - metals.