What determines the properties of an atom or molecule? 6 th Grade Gifted Chapter 4 – Chemical Reactions

Some factors that affect the properties of matter Element(s) (atomic structure) Number of each element present Bonding of the elements

How do atoms compare to one another? Atoms of the same element are similar to one another but different from atoms of different elements. Atoms of the same element have the same number of protons. They may or may not have the same number of total electrons, valence electrons, neutrons, electron shells, atomic mass. Atoms of different elements have a different number of protons.

Modified Bohr Models A modified Bohr model consists of the proper number of neutrons and protons in the nucleus. Electrons are placed in the electron cloud around the nucleus. A max of 2 electrons in the 1 st shell A max of 8 electrons in the 2 nd shell A max of 18 electrons in the 3 rd shell

Example Boron Atomic mass = 11 (round to nearest whole number) Atomic number = 5 #protons = 5 #electrons =5 #neutrons = 6

Group I

Compare these two elements Both have protons, electrons, and neutrons. Have same number of valence electrons. Have different numbers of protons, electrons, and neutrons.

Valence Electrons Electrons in the outermost shell. These electrons are involved in the bonding together of atoms to form molecules. Label the valence electrons on your diagram. How many valence electrons do the atoms in each group have?

Octet Rule Atoms are most stable when they have a full set of valence electrons. For most atoms full = 8 valence electrons. To get a full outer shell, atoms will give, take, or share electrons.

Metals Give electrons to nonmetals. When they give away electrons, they end up with more protons than electrons. They become a positively charged ion (cation). The cation is the most stable form of the atom.

Example 11 + and 11 - net charge = 011+ and 10 - net charge = +1

Sodium Ion 11 protons electrons10- Net charge+1 Na 1+

Nonmetals Take electrons from metals to get a full outer shell. When they take electrons, they end up with more electrons than protons. They become negatively charged ions (anions).

Example Cl atom: 17 + and 17 - Net Charge = 0 Cl ion: 17+ and 18- Net Charge = 1 -

Practice Determine the most stable form for the following atoms: Li Be B C N O F Na Mg Al Si P S Cl Do you see any patterns

So what happens when a Na and Cl atom are near each other?

NaCl Sodium gives one electron to Chlorine. Now both atoms are stable. Sodium has a 1 + charge and Chlorine has a 1 - charge. Opposite charges attract to form sodium chloride – NaCl. Notice that the 1 + and 1 - cancel each other to make a neutral compound.

Ca + Cl Calcium gives away 2 electrons to become stable One electron goes to one Chlorine and the other electron goes to the another chlorine. In the end, Mg has a 2 + charge and each Cl has a 1 _ charge. They combine to form MgCl 2. the compound is neutral.

Ionic Compound Two ions are held together by an ionic bond. The compound that is formed is called an ionic compound.

Nonmetals Nonmetals share electrons with other nonmetals to become stable. Since they share, neither atom gains or loses electrons, so neither atom has a charge. The sharing of electrons forms a covalent bond. The resulting compound is called a covalent or molecular compound.

Example

Use a dot structure Each dot or X represents 1 valence electron. Notice that each Cl atom needs one more electron to be stable. The line represents the bond (the sharing of 1 electron) – a single covalent bond.

O + O 2 shared electrons – double covalent bond

N + N 3 shared electrons – triple covalent bond

Properties of Ionic and CovalentCompounds Ionic

Respond Compare and contrast ionic and covalent bonding. Write your response in your ISN.

Respond How do differences in atoms affect how an atom bonds to other atoms?