Science

An atom of sodium has 11 electrons. Make a sketch of a sodium atom, showing how many electrons it has at each energy level. Infer how reactive sodium atoms are.

Electrons in the outermost energy level of an atom are called valence electrons. They determine many of the properties of an atom, including how reactive it is.

Which classes of elements make up ionic compounds?

Ionic compounds are named for their positive metal ion first, followed by their negative nonmetal ion.

What are some other substances that the property of flammability?

Substances called fuels have the properties of flammability. They include fossil fuels, coal, natural gas, and petroleum, as well as fuels mad from petroleum, such as gasoline and kerosene. Substance made of wood, such as paper and cardboard, are also flammable.

What do these 2 closets have to do with science?

They show why it's important to keep things organized including pure substance t hat make up all kinds of matter.

Define the chemical property called reactivity.

Reactivity is the ability of matter to react chemically with other substances.

What are the groups in Mendeleev's table?

The columns of the table, called groups, contained elements with similar properties.

What is the name of the ionic compound that is composed of positive barium ions and negative iodide ions?

The compound is named barium iodide

What is a covalent bond?

A covalent bond is the force of attraction that holds together two atoms that share a pair of valence electrons. Covalent bonds form only between atoms of nonmetals.

A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is?

A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can hold only eight electrons. This means that is outermost energy level is full. Therefore, a neon atom is very stable.

Why does sodium give up an electron?

An atom of a group 1 element such as sodium has just one valence electron. It is "eager" to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure below. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason.

Why does chlorine accept the electron from sodium?

An atom of a group 17 element such as chlorine has seven valence electrons. It is "eager" to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason.

Carbon (C) has four valence electrons. What does an electron dot diagram for this element look like?

An electron dot diagram for carbon looks like this

What is an ionic bond? How does it form?

An ionic bond is the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element.

Based on both periodic tables above (Figures above and above), what are examples of elements that have just one valence electron? What are examples of elements that have eight valence electrons? How many valence electrons does oxygen (O) have?

Any element in group 1 has just one valence electron. Examples include hydrogen (H), lithium (Li), and sodium (Na). Any element in group 18 has eight valence electrons (except for helium, which has a total of just two electrons). Examples include neon (Ne), argon (Ar), and krypton (Kr). Oxygen, like all the other elements in group 16, has six valence electrons.

How can you tell that wood ashes are a different substance than wood?

Ashes have different properties than wood. For example, ashes are gray and powdery, whereas wood is brown and hard.

Energy level III can hold a maximum of 18 electrons. How many orbitals does this energy level have?

At two electrons per orbital, this energy level must have nine orbitals.

What is atomic mass?

Atomic mass is the mass of an element. It is about equal to the mass of protons plus the neutrons in an atom.

What is an atom?

Atoms are the building blocks of matter. They are the smallest particles of an element that still have the element's properties.

Why do copper and carbon differ in their ability to conduct electricity?

Atoms of metals such as copper easily give up valence electrons. Their electrons can move freely and carry electric current. Atoms of nonmetals such as the carbon, on the other hand, hold onto their electrons. Their electrons can't move freely and carry current.

Which of the following statements is true about the atoms of any element?

Atoms of other elements have different numbers of subatomic particles, but the number of protons always equals the number of electrons

How many valence electrons do atoms of silicon and germanium have? What happens to their valence electrons when the atoms are exposed to an electric field?

Atoms of these two elements have four valence electrons. When the atoms are exposed to an electric field, the valence electrons move away from the atoms and allow current to flow.

Draw an electron dot diagram for an atom of Nitrogen (N)

Because valence electrons are so important, atoms may be represented by electron dot diagrams that show only their valence electrons.

Find calcium (Ca) in the periodic table (see Figure above). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react.

Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that "wants" to gain two electrons. This would be an element in group 6, such as oxygen.

All atoms of carbon have six protons. How many electrodes do they have?

Carbon atoms must have six electrons to "cancel out" the positive charges of six protons. That's because atoms are always neutral in electric charge.

What is a chemical property?

Chemical properties are properties that can be measured or observed only when matter undergoes a change to become an entirely different kind of matter. They include reactivity, flammability, and the ability to rust.

Which of the following represent molecules? Which represent compounds? Which represents a covalent compound?

Covalent bonds form because the shared electrons fill each atom's outer energy level and this is the most stable arrangement of electrons.

Lithium has three protons, four neutrons, and three electrons Sketch a model atom similar to the model above for helium.

Does your sketch resemble the model in the figure below. Three protons (blue) and four neutrons (grey) in the nucleus, with three electrons (red) moving around the nucleus.

Relate energy levels to the amount of energy their electrons have

Electron are always added to the lowest level first until it has the maximum number of electrons possible, and then electrons are added to the next higher energy level until that level is full, and so on

In the atomic model Figure above, where would you find electrons that have the most energy?

Electrons with the most energy would be found in energy level IV.

What do you think happens when an atom gains an electron and becomes a negative ion?

Energy is released when an atom gains an electron. Halogens release the most energy when they form ions. As a result, they are very reactive elements

What are energy levels

Energy levels (also called electrons shells) are fixed distances from the nucleus of an atom where electrons may be found. As you go farther from the nucleus, electrons at higher energy levels have more energy

What is flammability? Identify examples of flammability.

Flammability is the ability of matter to burn. Ex: Cardboard, gasoline, paper, trees

Now can you explain why calcium chloride prevents ice from forming on a snowy road?

If calcium chloride dissolves in water, it breaks down into its ions (Ca2+ and Cl-). When water has ions dissolved in it, it has a lower freezing point. Pure water freezes at 0°C. With calcium and chloride ions dissolved in it, it won't freeze unless the temperature reaches -29°C or lower.

How did Mendeleev develop his periodic table of element?

In 1869, Dmitri Mendeleev developed a method for organizing elements based on their atomic mass. His method was later revised, but it served as a basis for the method used today.

Why do metals lose electrons and nonmetals gain electrons in the formation of ionic bonds?

Ionic bonds form only between metals and nonmetals. That's because metals "want" to give up electrons, and nonmetals "want" to gain electrons.

Describe properties of Ionic Compounds

Ionic compounds are solids with high melting and boiling points. They are good conductors of electricity but only when dissolved in water. Their crystals are rigid and brittle.

What is an ionic compound?

Ionic compounds consist of oppositely charged ions that are held together by ionic bonds. The opposite charges cancel out so ionic compounds have a net neutral charge. Ionic compounds form when metals transfer valence electrons to nonmetals

What are crystals

Ionic compounds exist as crystals rather than molecules. A crystal consists of many alternating positive and negative ions bonded together in a matrix.

The ionic compound sodium fluoride is added to toothpaste to prevent tooth decay. Describe the composition and structure of this compound.

Ionic compounds have many uses in industry. They are also needed by humans and other living things.

Why might it be a good basis for organizing elements ?

It is a good basis for organizing elements because each elects has a unique number of protons and atomic mass is an indirect way of organizing elements by number of protons

Atoms of lithium (Li) and cesium (Cs) both lose electrons and become positive ions when they from ionic bonds. Which type of atom requires more energy to become an ion? Why?

It takes energy to remove valence electrons from an atom and form a positive ion. Energy is released when an atom gains valence electrons and forms a negative ion.

Describe the periods in Mendeleev's table.

Mendeleev created a periodic table of all the elements that were known at the time. The rows of the table, called periods, each contained eight elements that increased in atomic mass from left to right.

Why was Mendeleev's periodic table a good model?

Mendeleev's periodic table was a good model because it could be used to predict unknown elements and their properties. All of these missing elements were eventually discovered.

Predict what other elements might form ionic bonds

Metals on the left and in the center of the periodic table form ionic bonds with nonmetals on the right of the periodic table. For example, alkali metals in group 1 form ionic bonds with halogen nonmetals in group 17

Why can't nonmetals conduct electricity?

Metals, which easily give up electrons, can conduct electricity. Nonmetals, which attract electrons, generally cannot. Metalloids such as silicon and germanium can conduct electricity but not as well as metals

Which element in the figure above has the biggest atoms?

The element in the figure with the biggest atoms is Cesium (CS)

Which element would you expect to be more reactive: Phosphorus (P) or Fluorine (F)

The number of valence electrons in atoms may cause them to be unreactive or highly reactive. For those atoms that are reactive, the number of valence electrons also determines whether they tend to give up or gain electrons in chemical reactions.

How many valence electrons does the oxygen atom (O) share with each hydrogen atom (H)? How many covalent bonds hold the water molecule together?

The oxygen atom shares one pair of valence electrons with each hydrogen atom. Each pair of shared electrons represents one covalent bond, so two covalent bonds hold the water molecule together.

Nitrogen is a diatomic element with five valence electrons. Create a model of a molecule of nitrogen.

The two atoms that are held together in a covalent bond may be atoms of the same element or different elements. When atoms of different elements bond together, it forms a covalent compound.

How many electrons do these two oxygen atoms share? How many covalent bonds hold the oxygen molecule together?

The two oxygen atoms share two pairs of electrons, so two covalent bonds hold the oxygen molecule together.

Which of the following statements about valence electrons and the periodic table is true?

Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with other atoms.

Explain why atoms are always neutral in charge?

electrons have an equal number to protons to "cancel out" the positive charges of the six protons. That's because atoms are always neutral in electric charge.