What periods Cannot have expanded octets?
An element from Period 3 and below will be able to expand octet by making use of its energetically accessible, or low lying d-subshell for bonding. This means only Period 2 elements such as C, N, O and F cannot expand octet and have to obey octet rule.
some common examples of elements with expanded octets are sulfur, phosphorous, silicon and chlorine. These 4 elements are in the p block of period 3. elements before silicon cannot have an expanded octet because they are only occupying the s and p orbitals.
However, there are three general exceptions to the octet rule: Molecules, such as NO, with an odd number of electrons; Molecules in which one or more atoms possess more than eight electrons, such as SF6; and. Molecules such as BCl3, in which one or more atoms possess less than eight electrons.
Helium and hydrogen are exceptions to the octet rule, and some say the “duet rule” applies. H and He are stabilized with 2 electrons, not an octet.
Hydrogen, beryllium, and boron have too few electrons to form an octet. Hydrogen has only one valence electron and only one place to form a bond with another atom. Beryllium has only two valence atoms, and can form only electron pair bonds in two locations. Boron has three valence electrons.
Expansion of octet is possible only from Period 3 elements onwards, due to the presence of low-lying empty d orbitals that can accommodate the extra electrons.
The metals in Groups 3 to 12 can obey the octet rule, but they are not required to do so. They have d electrons that they can use to put more than eight electrons in their valence shell ("expand their octet"). For example, Fe has the electron configuration [Ar]4s²3d⁶.
You can often identify expanded octet by the S = N-A rule. When this "rule" suggests that you need fewer bonds than needed to put together the skeleton structure, then you need expanded octet.
All of non-metals and metalloids that are not explicitly listed above are able to achieve octets when bonding, but can also deviate from the "octet rule" by expanding their valences to accommodate more than eight electrons.
The octet rule is applicable only for atoms in their ground state. It does not take account into the number of electrons in an atom. It failed to explain the relative stability of molecules. The shape of the molecule is not predicted by the octet rule.
Which of the following does not allow octet rule?
The two elements that most commonly fail to complete an octet are boron and aluminium; they both readily form compounds in which they have six valence electrons, rather than the usual eight predicted by the octet rule.
Since the first shell can only accommodate two electrons, elements such as lithium, helium, and hydrogen obey the duet rule instead of the octet rule.
Oxygen has no empty orbital in quantum 2, so cannot excite and 'spread' its electrons, so cannot bond these to form an expanded octet.
Which element(s) does not follow the octet rule? *The two elements that most commonly fail to complete an octet are boron and aluminum, both of which readily form compounds in which they have six valence electrons, rather than the usual eight predicted by the octet rule.
The problem with this structure is that boron has an incomplete octet; it only has six electrons around it. Hydrogen atoms can naturally only have only 2 electrons in their outermost shell (their version of an octet), and as such there are no spare electrons to form a double bond with boron.
Expanded Octets
Starting with the third period, the d sublevel becomes available, so it is possible to use these orbitals in bonding, resulting in an expanded octet. Phosphorus and sulfur are two elements that react with halogen elements and make stable compounds with expanded octets.
The most common examples are the covalent compounds of beryllium and boron. For example, beryllium can form two covalent bonds, resulting in only four electrons in its valence shell: Formally, the P atom has 10 electrons in its valence shell.
Elements in the third period and below can accommodate more than an octet of electrons. Although elements such as Si, P, S, Cl, Br, and I obey the octet rule in many cases, under other circumstances they form more bonds than the rule allows.
In SF4 the central S atom has in all 10 electrons around it, while each F atom has eight. Thus S atom in SF4 does not obey the octet rule.
Atoms of the second period cannot have more than eight valence electrons around the central atom. However, atoms of the third period and beyond are capable of exceeding the octet rule by having more than eight electrons around the central atom.
Can potassium have an expanded octet?
Answer and Explanation: FALSE. The statement is false because if we look at the electronic structure of potassium, we find that it only has one electron in its valence shell. According to the Octet rule, the elements that have atomic numbers less than 20 follow the octet rule.
9.37 If fluorine formed seven covalent bonds with other atoms, it would effectively have a fourteen electrons, an expanded octet. Fluorine is a period 2 element, however, and its outermost shell (n = 2) only has an s subhshell and a p subshell. This shell can only hold eight electrons total.
Note that in the Lewis structure for BrF5, Bromine (B) is in Period Four on the periodic table. This means it can hold more than eight valence electrons. This is called an expanded octet.
Iodine is below Period Two on the periodic table so it can have an expanded octet (hold more than eight valence electrons).
Illustrated Glossary of Organic Chemistry - Octet rule. Octet rule: The concept that compounds containing carbon, nitrogen, oxygen, and fluorine are more stable if these atoms have eight valence electrons.
The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds. When discussing the octet rule, we do not consider d or f electrons.
Which of the following is an exception to the octet rule? Sulfur in SO2−4 is an exception to the octet rule.
The bonding in carbon dioxide (CO2): all atoms are surrounded by 8 electrons, fulfilling the octet rule.
The first exception to the Octet Rule is when there are an odd number of valence electrons. An example of this would be Nitrogen (II) Oxide also called nitric oxide (NO. Nitrogen has 5 valence electrons while Oxygen has 6. The total would be 11 valence electrons to be used.
No, some of the p-block elements simply don't follow the octet rule. For instance, sulfur, in combination with hydrogen, forms a molecule called dihydrogen sulfide which is similar to water. Here, sulfur obeys the octet rule by forming two lone pairs around the central sulfur atom and two bonds with hydrogen.
Can xenon have an expanded octet?
Elements of the 3rd period and onwards are capable of showing expanded octet while bonding. Phosphorus (P), Krypton (Kr), and Xenon (Xe) belong to the 3rd, 4th, and 5th periods respectively. They have d and f orbitals for further expansion of their valence shell. Hence, they are capable of expanding their octets.
Exception 3: Expanded Valence Shells
Hence, the third period elements occasionally exceed the octet rule by using their empty d orbitals to accommodate additional electrons.
Expansion of the valence shell is impossible for an atom in the second period because there is no such thing as a 2 d orbital. The valence (n = 2) shell of nitrogen, for example, consists of the 2s and 2p subshells only. Thus nitrogen can form NF3 (in which nitrogen has an octet) but not NF5.
Atoms with an expanded octet
Phosphorous often has 5 orbitals (10 electrons) and sulfur often has 6 orbitals (12 electrons) because they are in the third period, but nitrogen and oxygen can never have expanded octets because they are in the second period and there is not such thing as a 2d orbital.
Carbon has 6 electrons, two in its inner shell and four in its valence shell. When carbon takes four electrons from other atoms, in which it forms ionic bonds, it has a full valence shell, so it is unable to from any more bonds.
Expanded octet (hypervalent): A valence shell electron count that exceeds eight electrons. In methane (CH4), carbon has a full octet (eight valence electrons). In phosphate ion (PO43-), each oxygen has a full octet (eight valence electrons), whereas phosphorus has an expanded octet (ten valence electrons).
Which element(s) does not follow the octet rule? *The two elements that most commonly fail to complete an octet are boron and aluminum, both of which readily form compounds in which they have six valence electrons, rather than the usual eight predicted by the octet rule.
mono, di, tri, tetra, penta, hexa, septa, octa, nona.
In particular, you'll find expanded octet in odd compounds made from the larger noble gases as well as some of the halogens (in period 3 and greater).