“This is one of the very few studies in general of epigenetic acceleration in children, and the very first cohort in the world looking at prenatal phthalate exposure,” said Nina Holland, a co-author and research professor emeritus of environmental health. This study, recently published online ahead of print in Environmental Research, is the first evidence that prenatal exposure to DEHP, a common phthalate, is also associated with decreased epigenetic age acceleration at age seven meaning that the boys’ development lagged behind their chronological age. They have long been known to disrupt the endocrine system, which can set the stage for a wide range of developmental and health problems. The chemicals, called phthalates, are widely used in personal care products such as shampoo, hair spray, and soap, as well as plastic packaging and other consumer goods. This will take you to the main part of Chemguide.Boys exposed to a group of common chemicals while still in the womb may experience slowed development in childhood, according to a new study by researchers at UC Berkeley School of Public Health. To return to the list of all the CIE sections To return to the list of learning outcomes in Section 9.5 That means that you can fit a lot more iron atoms into a given volume than calcium atoms. The radius of a calcium atom is 0.197 nm the radius of an iron atom is only 0.126 nm. Iron atoms are significantly smaller than calcium atoms. The relative atomic mass of calcium is 40, but the RAM of iron is 56, for example. Iron is fairly typical with a density of 7.89 g cm -3.Īs you go across the period, the atoms get heavier. The transition elements have higher densities than calcium. Zinc's 3d electrons aren't involved because the 3d level is then full.Ĭalcium's density is quite low at 1.54 g cm -3. With scandium and the transition metals, 3d electrons are involved as well. In calcium, only the 4s electrons are involved. This is because one of the factors which control melting point is the number of electrons which are involved in the metallic bond. All of the transition metals following it in the Periodic Table have higher melting points (apart from zinc, which doesn't count as a transition metal). (In fact the modern IUPAC definition of a transition element would include scandium, but that isn't what the CIE syllabus is using.)Ĭalcium's melting point is variously quoted as 839☌ or 842☌. Remember that the d-block elements include everything from scandium to zinc, but scandium and zinc themselves don't count as transition elements. The syllabus actually compares calcium with the transition metals, but there are several cases where it is easier to compare it with the whole of the first row of d-block elements - especially for explanations. The syllabus quotes calcium for comparison purposes because it is immediately before the first transition series in the Periodic Table. This statement asks you to compare the melting point and density of a typical transition metal with a non-transition metal like calcium.īefore you go on, you should find and read the statement in your copy of the syllabus. Chemguide: CIE A level chemistry support: Learning outcome 9.5(c)Ĭhemguide: Support for CIE A level Chemistry
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