Answer:
- <u>Tellurium (Te) and iodine (I) are two elements </u><em><u>next to each other that have decreasing atomic masses.</u></em>
Explanation:
The <em>atomic mass</em> of tellurium (Te) is 127.60 g/mol and the atomic mass of iodine (I) is 126.904 g/mol; so, in spite of iodine being to the right of tellurium in the periodic table (because the atomic number of iodine is bigger than the atomic number of tellurium), the atomic mass of iodine is less than the atomic mass of tellurium.
The elements are arranged in increasing order of atomic number in the periodic table.
The atomic number is equal to the number of protons and the mass number is the sum of the protons and neutrons.
The mass number, except for the mass defect, represents the atomic mass of a particular isotope. But the atomic mass of an element is the weighted average of the atomic masses of the different natural isotopes of the element.
Normally, as the atomic number increases, you find that the atomic mass increases, so most of the elements in the periodic table, which as said are arranged in icreasing atomic number order, match with increasing atomic masses. But the relative isotope abundaces of the elements can change that.
It is the case that the most common isotopes of tellurium have atomic masses 128 amu and 130 amu, whilst most common isotopes of iodine have an atomic mass 127 amu. As result, tellurium has an average atomic mass of 127.60 g/mol whilst iodine has an average atomic mass of 126.904 g/mol.
Answer:
Covalent network solids are formed by networks or chains of atoms or molecules held together by covalent bonds. Consists of sp3 hybridized carbon atoms, each bonded to four other carbon atoms in a tetrahedral array to create a giant network. Examples of network covalent solids include diamond and graphite (both allotropes of carbon), and the chemical compounds silicon carbide and boron-carbide.
When water is in liquid form its molecules are free to move around.
Water molecules are packed reasonably close together. However when water freezes its molecules take up a hexagonal lattice (repeating structure) which has space in the middle of it.
This is largely due to hydrogen bonding between water molecules (complicated).
As a result water molecules in ice aren't packed as closely together as they are in liquid water so the density of ice is lower than that of liquid water.
Hope that helps. I doubt you need to know about hydrogen bonding.
