Chapter 5… Where we get to learn about how elements are arranged in the periodic table… No, you don’t have to memorize the whole table. Just some of it.

Thing we’ll learn today (5.1) 1.How Mendeleev first arranged elements in his table. 2.How the modern periodic table is arranged. 3.How the modern periodic table demonstrates periodic law (just as Mendeleev’s did.)

The surface of a silicon chip

Let’s inspect that ol’ table Examine your periodic table copy. What do you notice about its arrangement?

Gold and silver have similar properties. These elements are located in the same column of the periodic table.

It’s the 1860s… Scientists knew some of the chemical and physical properties of more than 60 elements. (How many are there today?) But there was no general system of organizing them. Scientists studied the elements and their properties to find a way to get them in order.

Dmitri Mendeleev Dmitri Mendeleev, a Russian chemist, was one of the first scientists to design a way of organizing the elements. He is generally considered the “father” of the periodic table.

Talk about OCD! Mendeleev listed the properties of each element on a separate piece of paper then tried to arrange the pieces of paper in rows and columns so that they formed a pattern. He found that if the elements were listed by increasing atomic mass, certain properties appeared at certain intervals within the list. He was on to something!

1869, it is published Mendeleev published the first periodic table of the elements in In his table, he arranged elements in rows by increasing atomic mass. Sure enough, for any column, all of the elements in that column had similar properties.

He even predicted elements not discovered. Check it out – no noble gases!

Question marks meant… The question marks represented elements with certain properties that hadn’t been discovered yet. Mendeleev saw patterns of chemical properties and predicted that scientists would eventually find the elements that filled those gaps.

He predicted germanium and in 1886, it was discovered.

He wasn’t the only one, but he was the first to make predictions. Other people were developing their own periodic tables around this same time, but Mendeleev was the first to use the table to make predictions. And be right about it! He’s considered the father of the periodic table and the element mendelevium is named in his honor.

Find a friend. Ask a question. 1.How did Mendeleev organize the elements? 2.Why did Mendeleev leave gaps in the periodic table?

Find a friend. Ask a question. 1.How did Mendeleev organize the elements? By increasing atomic mass. He started a new row each time the chemical properties repeated. 2. Why did Mendeleev leave gaps in the periodic table? He left gaps for new elements that he predicted would be discovered. The gaps were needed to make his patterns work out correctly.

A few elements didn’t fit the pattern. For example, Mendeleev had to place tellurium before iodine in his table so they fit the pattern of chemical properties. However, when he made the switch, Te and I were no longer in order of increasing atomic mass. Oh my.

Enter Henry Moseley. English chemist extraordinaire.

Moseley broke the code. The problem with the atomic mass discrepancy was finally solved about 40 years later by Henry Moseley. Unlike Mendeleev, Moseley didn’t arrange the elements by increasing atomic masses. Instead, he organized them by atomic number.

The modern periodic table Remember that an element’s atomic number is the number of protons in an atom of the element. Interestingly, this way of organizing didn’t change the locations of most elements. In fact, now the whole Te and I situation could be resolved. Finally!

Tellerium has a higher atomic mass than iodine, but it has a lower atomic number. Moseley could keep them in place without disturbing the pattern of chemical properties. The explanation? Isotopes!

Periodic law The modern periodic table organizes elements by atomic number. When elements are arranged in this way, elements that have similar properties appear at regular intervals. This principle is known as the periodic law.

Find a friend. Ask a question. 1.Why did Mendeleev have problems arranging the elements Te and I? 2.What property did Moseley use to organize the modern periodic table?

Find a friend. Ask a question. 1.Why did Mendeleev have problems arranging the elements Te and I? Te and I did not fit the pattern of chemical properties unless they were put in the wrong order of atomic mass. 1.What property did Moseley use to organize the modern periodic table? Atomic number

Periods and Groups A horizontal row on the periodic table is called a period. There are seven periods on the periodic table. The properties of the elements in a period are different.

Example… Moving left to right, elements become less metallic.

A vertical column on the periodic table is called a group. All the elements in a group have similar chemical properties.

Helium and neon, in group 18, are both unreactive elements. Under normal conditions, these elements don’t bond with other elements to form compounds.

Find a friend. Ask a Question. 1.Which information helps you predict the properties of an element—the period it is in, or the group it is in? Explain your answer. 2.Titanium, arsenic and bromine are in Period 4. Which is most metallic, and which is least metallic?

We’ll learn more about these patterns The color coded categories of elements are associated with certain groups. We’ll learn more about these groups and their properties. YAY! In the mean time, you need to memorize the symbol and names for the first 36 elements on the periodic table.

Target questions 1.Using your periodic table, identify the following: a. the symbol for mercury b. the period and group of gold c. the atomic mass of iron d. the atomic number of neon e. the element represented by Cu