Chp. 5 Science

Alkaline Earth Metals

- All alkaline earth metals have two valence electrons. - Metals in Group 2A are harder than metals in Group 1A. The melting point of magnesium is 650 degree Celsius, which is much higher than the melting point of Sodium -98 degree Celsius. - Differences in reactivity among the alkaline earth metals are shown by the ways they react with water.

The Carbon Family

- Group 4A contains a nonmetal (carbon), two metalloids ( silicon and germanium), and two metals (tin and lead). Each of these elements has four valence electrons. - Notice that the metallic nature of elements increases from top to bottom within the group. Germanium is a better conductor of electric current than silicon. -Except for water, most of the compounds in your body contain carbon. - Silicon is the second most abundant element is Earth's crust. The clay used to produce this pottery contains silicon compounds called silicates.

The Nitrogen Family

- Group 5A contains two nonmetals (nitrogen and phosphorus), two metalloids ( arsenic and antimony), and one metal (bismuth). -Group 5A includes elements with a wide range of physical properties. Nitrogen is a nonmetal gas, phosphorus is a solid nonmetal, and bismuth is a dense metal. All of the elements in Group 5A have five valence electrons. - When air is cooled, the oxygen condenses before the nitrogen because nitrogen has a lower boiling point than oxygen. Much of the nitrogen obtained from air is used to produce fertilizers.

Evidence Supporting Mendeleev's Table (Continued)

- In 1875, a French chemist discovered a new element. He named the element gallium (Ga) in honor of France. Gallium -is a soft metal, -has a melting point 29.7 degree C, and -has a density of 5.91 g/cm cubed. - The properties of gallium are remarkably similar to the predict properties of eka- aluminum. Scientists concluded that gallium and eka- aluminum are the same element. - The discovery of scandium (Sc) in 1879 and the discovery of germanium (Ge) in 1886 provided more evidence.

The periodic table presents three different ways to classify elements.

- State: solid, liquid, and gas - Occurrence in nature: natural or not - General properties: metal, non-metal, metalloids.

Evidence Supporting Mendeleev's Table

- The close match between Mendeleev's predictions and the actual properties of new elements showed how useful his periodic table could be. - Mendeleev named missing elements after elements in the same group. He gave the name eka- aluminum to the missing element one space below aluminum in the table (eka meaning "one") Mendeleev predicted that eka-aluminum would be a soft metal, have a low melting point, and have a density of 5.9 g/cm cubed.

The Halogens

- The elements in Group 7A are called Halogens. Each halogen has seven valence electrons. At room temperature, chlorine is a gas, bromine is a liquid, and iodine is a solid. -Despite their physical differences, the halogens have similar chemical properties.

Atomic Mass Units

- The mass of an atom in grams is extremely small. In order to have a convenient way to compare the masses of atoms, scientists chose one isotope to serve as a standard. - Scientists assigned 12 atomic mass units to the carbon-12 atom, which has 6 protons and 6 neutrons. An atomic mass unit (amu) is defined as one twelfth the mass of carbon-12 atom.

Transition Metals

- The metals in groups 3 through 12 are called transition metals. Transition metals are elements that form a bridge between the elements on the left and right sides of the table. - Transition elements, such as copper and silver, were among the first elements discovered. -One property of many transition metals is their ability to form compounds with distinctive colors.

Valence Electrons

- When the A groups in the periodic table are numbered from 1 through 8, the group number matches the number of valence electrons in the electron configuration of an element in that group. - Valence electrons play a key role in chemical reactions. - Properties vary across a period because the number of valence electrons increases from left to right. - Elements in a group have similar properties because they have the same number of valence electrons. The properties are not identical because they valence electrons are in different energy levels. - Because hydrogen has a single valence electron, it is grouped with other elements, such as lithium, that have only one valence electron.

Variation Across a Period

-Across a period from left to right, the elements become less metallic and more nonmetallic in their properties. -From left to right across Period 3, there are three metals (Na, Mg, and Al), one metalloid (Si), and four nonmetals (P, S, Cl, and Ar). - Sodium reacts violently with water. - Magnesium will not react with water unless the water is hot. - Aluminum does not react with water, but it does react with oxygen. - Silicon is generally unreactive. -Phosphorus and sulfur do not react with water, but they do react with oxygen. -Chlorine is highly reactive.

Calcium

-Calcium carbonate- a compound of calcium, carbon, and oxygen-- is the main ingredient in chalk, limestone, and coral. - Magnesium and calcium have essential biological functions, and they provide materials used in construction and transportation.

The Boron Family

-Group 3A contains the metalloid boron, the well known metal aluminum, and three less familiar metals (gallium, indium, and thallium). - All these elements have three valence electrons. -Aluminum is the most abundant metal Earth's crust. - A compound of boron, silicon, and oxygen is used to make glass that does not shatter easily when its temperature changes rapidly. Glass that contains boron is used to make laboratory glassware and cookware that can go directly from the oven to the refrigerator.

Periods

-Lithium, the first element in Period 2, has one electron in its second energy level. - Sodium, the first element in Period 3, has one electron in its third energy level. - This pattern applies to all the elements in the first column on the table.

Mendeleev's Proposal

-Mendeleev made a "deck of cards" of the elements, listing an element's name, mass, and properties on each card. When Mendeleev lined up the cards in order of increasing mass, a pattern emerged. The key was to break the elements into rows. -The final arrangement was similar to a winning arrangement in solitaire, except that the columns were organized by properties instead of suits. Within a column, the masses increased from top to bottom. -Mendeleev's chart was a periodic table.

Mendeleev's Prediction

-Mendeleev was able to offer the best explanation for how the properties of an element were related to its location in his table. - Mendeleev was confident that the gaps in his table would be filled by new elements. He used the properties of elements located near the blank spaces in his table to predict the properties for undiscovered elements. - Some scientists didn't accept those predictions. Others used the predictions to help in their search for undiscovered elements.

Metalloids

-Metalloid elements are located on the periodic table between metals and nonmetals. - Metalloids are elements with properties that fall between those of metals and nonmetals. - For example, a metalloid's ability to conduct electric current varies with temperature. Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.

Nonmetals

-Nonmetals generally have properties opposite to those of metals. -Nonmetals are elements that are poor conductors of heat and electric current. -Nonmetals have low boiling points-many nonmetals are gases at room temperature. -Nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble. -Fluorine is the most reactive nonmetal. The gases in Group 18 are the least reactive elements in the table. Some toothpastes use a compound of the nonmetal fluorine and the metal sodium to help tooth decay.

Nobel Gases

-The elements in Group 8A are called nobel gases. Helium has two valence electrons. Each of the other noble gases has eight valence electrons. - When electric current passes through noble gases, they emit different colors. Helium emits pink, neon emits orange-red, argon emits lavender, krypton emits white, and xenon emits blue.

Metals

-The majority of the elements on the periodic table classified as metals. Metals are elements that are good conductors of electric current and heat. - Except for mercury, metals are solids at room temperature. -Most metals are malleable. -Many metals are ductile; that is, they can be drawn into thin wires.

Alkali metals

-These metals have a single valence electron and are extremely reactive. Because they are so reactive, alkali metals are found in nature only in compounds. - Sodium reacts violently with water and releases enough energy to ignite the hydrogen gas that is produced. - Sodium and potassium are stored under oil to keep them from reacting with the oxygen and water vapor in air. - Cesium is so reactive that it is usually stored in a sealed glass tube containing argon gas.

Until 1750s, scientists had identified only ____ elements, mainly metals, such as copper and iron. As the number of known elements grew, so did the need to organize them into groups based on their properties.

17

The elements in Group _____ are called alkaline earth metals.

2A

The elements in Group 1A are called ________________.

Alkali metals

In the 1860s, __________ developed an approach for organizing the elements while playing the card game solitaire. In this game, the player sorts a deck of cards by suit and value.

Dmitri

How is the modern periodic table organized?

Elements are arranged by increasing atomic numbers (numbers of protons).

What categories are used to classify elements on the periodic table?

Elements are classified as metals, non-metals, and metalloids.

The Oxygen Family

Group 6A has three nonmetals (oxygen, sulfur, and selenium), and two metalloids ( tellurium and polonium). All the elements in Group 6A have six valence electrons. - Oxygen is the most abundant element in Earth's crust.

How did Mendeleev arrange the elements?

He arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.

____________ is the first element in Period 1, has one electron in its first energy level.

Hydrogen

The Search for Order

In 1789, Antoine Lavoisier grouped the known elements into categories he called metals, nonmetals, gases, and earths. For the next 80 years, scientists looked for different ways to classify the elements. But no system worked for all the known elements.

Isotopes of Chlorine

In nature, most elements exist as a mixture of two or more isotopes. The element chlorine has an atomic mass of 35.453 amu. Where does the number 35.453 come from ? - There are two natural isotopes of chlorine, chlorine- 35 and chlorine-37. - An atom of chlorine-35 has 17 protons and 18 neutrons. - An atom chlorine-37 has 17 protons and 20 neutrons.

Periodic Table

Is an arrangement of elements in columns, based on a set of properties that repeat form row to row.

What does the atomic mass of an element depend on?

It depends on the distribution, of an element's isotopes in nature and the masses of those isotopes.

Magnesium

Magnesium plays the key role is photosynthesis. The compound at the center of this process is chlorophyll, and at the center of chlorophyll is a magnesium atom. - A mixture of magnesium and other metals can be as strong as steel, but much lighter. The frames of bicycles and backpacks often contain magnesium.

Within a period of the periodic table, how do the properties of the elements vary?

Metallic characteristics decrease from left to right

Magnesium plays a key role in ________________________.

Photosynthesis

Why do the elements in a group have similar properties?

They have the same number of valence electrons

Why do elements in a group have similar chemical properties?

They have the same number of valence electrons.

Which of the following is not characteristic of metals?

brittle

The elements in a group have similar electron configurations, so members of a group in the periodic table have similar ______________________________.

chemical properties

For which element did Mendeleev correctly predict the properties even before it had been discovered?

gallium

Each column in the periodic table is called a _________.

group

In Mendeleev's periodic table, elements with similar properties were grouped

in the same column.

Each row in the table of elements is a __________.

period

This pattern of repeating properties is the __________________.

periodic law

At the time Mendeleev made his table, many elements had not yet been discovered. When he placed the elements where their properties fit, there were ____________________ in the table.

several gaps

What determines the atomic mass of an element?

the natural distribution of isotopes and the masses of those isotopes.